Il'gynoth told us the truth.

[pacotaco]

To find him, drown yourself in the circle of stars.
The Circle of Stars is the prison of N'zoth, in the depths of the ocean.

The king of diamonds has been made a pawn.
N'zoth manipulated Magni and us to use the Hearth to release him.

The lord of ravens will turn the key.
I'm starting to think this is Medivh. In the recent events, we learn that Wrathion seeks a way to protect the Dragonflights from the corrupting voices of N'zoth, and he ends up in Karazhan, where Medivh helps him.
Maybe N'zoth is counting on Medivh doing something and end up as another pawn, like Magni?

The boy-king serves at the master's table. Three lies will he offer you.
This is still a mystery to me. It seems to refer to Anduin, and probably means that he's another pawn, but I don't recall anything in particular that could be considered a lie.

Her heart is a crater, and we have filled it. First time we heard this we though it meant Azeroth. Now I'm pretty sure it meant Sylvannas. Since her death, over the years, she sees how all she loved is lost: her homeland, Silvermoon; her sisters' love; her hope to savethe Forsaken from extintion.
Seems like she found something that led her to the Old Gods and some promises we still don't know.

Five keys to open our way. Five torches to light our path.
Xal'atath refers to us as "the Opener... the Bringer of Truths... the Torch That Lights the Way!".
Opener: as in we use the Heart of Azeroth (the key) to open N'zoth's prison.
Bringer of Truths: as in freeing N'zoth we lead to Sylvannas revealing the truth, that she plotted with Azshara to start a war and use us all to free N'zoth.
The torches are not things like we though. They are people.

At the hour of her third death, she will usher in our coming.
Helya is the only one that comes to mind that she already died twice and is still around.

[B]From the earth, he draws strength. Our earth. Our strength.
Probably Wrathion.

Its surface blazes bright, masking shadows below.
X'era, or maybe another naaru we'd meet in the future.

[Xaviaton]

Five keys to open our way. Five torches to light our path.
Xal'atath refers to us as "the Opener... the Bringer of Truths... the Torch That Lights the Way!".
Opener: as in we use the Heart of Azeroth (the key) to open N'zoth's prison.
Bringer of Truths: as in freeing N'zoth we lead to Sylvannas revealing the truth, that she plotted with Azshara to start a war and use us all to free N'zoth.
The torches are not things like we though. They are people.

I have started wondering if this can have something to do with the Five Dragonflights uniting their power in the Heart of Azeroth as well.

[Skirdus]

We only know the exact nature of the first two for certain. The rest are utter speculation until we get concrete evidence that it's in fact what Il'gynoth is referring to. For instance, Alleria specifically recalls how she feels like she's "died twice" at one point. It's very much on the head, but it's certainly worth noting

[Throwme]

The lord of ravens will turn the key.
think
Maybe

The boy-king serves at the master's table. Three lies will he offer you.
still a mystery

Her heart is a crater, and we have filled it.
pretty sure

From the earth, he draws strength. Our earth. Our strength.
Probably

Its surface blazes bright, masking shadows below.
maybe

That's a lot of uncertainty for something you claim to be the truth. There can be no doubt about the truth, this is only speculations.

[Hey There Guys its Metro]

Man whatever else people say about the lore, the fact that people have had countless speculation sessions on what those words mean, and years later we STILL aren't sure, really says something right?

All I know is used to never care about lore in this game at all.
When I heard all the speculation around Ilgynoth, a seemingly random boss in one of the easiest raids ever, it was like the switch was flipped.

Now I can't get enough of the old god stuff!

[Shakana]

[B]From the earth, he draws strength. Our earth. Our strength.
Probably Wrathion.

You forgot to put [/ B] there

Anyway good post

[Cosmic Janitor]

I have started wondering if this can have something to do with the Five Dragonflights uniting their power in the Heart of Azeroth as well.

That would have been my guess as well, especially with us dumping their essence into the heart.

[Khaza-R]

The boy-king serves at the master's table. Three lies will he offer you.
This is still a mystery to me. It seems to refer to Anduin, and probably means that he's another pawn, but I don't recall anything in particular that could be considered a lie.

This quotes has to be taken into context with another quote

Six seats at the high table. Six mouths that hunger. One will consume all others.

The table that N'zoth refers to are the cosmic powers. Anduin serving that the table just means he serves one of seats. Which we know is the Light.

Its surface blazes bright, masking shadows below.
X'era, or maybe another naaru we'd meet in the future.

This one is just referring to the ocean and N'zoth's prison beneath the waves

[Nyel]

Its surface blazes bright, masking shadows below.
X'era, or maybe another naaru we'd meet in the future.

This could refer to Anduin as well. Especially when we consider that this line is also referencing him: "The boy-king serves at the master's table. Three lies will he offer you." Anduin is too good to be true, to perfect. That makes him susceptible for corruption (through the Void).

[Relapses]

I guess you could say he Il'gynoth tell a lie.

Oh, should I see myself out?

[Tyron]

Five keys to open our way. Five torches to light our path.

I think this refers to the dragonflights empowering the HoA and using it to free N'Zoth.

Its surface blazes bright, masking shadows below.

This is probably the sunwell. When Alleria visited the sunwell void energies started to come out of it, reacting to her.

[Count Zero]

At the hour of her third death, she will usher in our coming.
Helya is the only one that comes to mind that she already died twice and is still around.

Sylvanas has died thrice (when she was made a Banshee, when she ragequit off ICC, and when Godfrey one-shot her), but this probably isn't referring to her.

Azshara - when she was made a Naga (questionable if this is a "death"), when we defeated her in TEP, and possibly when we defeat her again in Ny'alotha.

[formerShandalay]

I think the 5 torches are the dragon essences we put into the heart. The dragons are all in some way connected (having been manipulated, influenced or simply tormented by them) to the Old Gods and the Old Gods in my opinion can use this to show them the way and an entrance to the heart of Azeroth. If you take it more literally an actual entrance to the heart chamber.

Her heart is a crater and we have filled it, I also think that's Sylvanas. But in a different way. I think that the rage she herself gets so annoyed at sometimes, because she can't control it, which is the only emotion that has not dimmed but grown stronger after her death and becoming a Banshee, is the Old Gods' doing. They may not have been able to do anything more to her (because she was raised as a Scourge undead), but they could tip the scale a little. This rage ensures that all of her cold planning at some point falls apart, because the rage takes over and she slips up.
If you take the quote more literal: all of her emotions vanished, which constitutes the crater in her heart, and were replaced by rage, which the Old Gods filled the crater with.

The six seats at the High Table I think are Life, Light, Disorder, Death, Shadow and Order and, with Sylvanas's words about the "Hungering Darkness" and "Death" I now think that the one to consume them all will be Death.

My guess for the bright surface with the Shadows below is the Sunwell. I think if we take the other line about the Light making a deal with the enemy of all into account the 'shadows below' may not even refer to the void or any of that, but to, again, the Hungering Darkness of Death. We've recently seen the Sunwell being a fountain of death, in the Scenario of the Bloodelven racial armor (as a memory from the time of the Scourge invasion into Quel'thalas). It could become one again.


Edit:
And the Lord of Ravens is Medivh in my opinion. Something in his talks with Wrathion will have triggered a response from Wrathion upon which he acts without due thought, or maybe Medivh even convinces him to do something that the Old Gods anticipate and want.
Or this has already accured and it has nothing to do with Wrathion but instead was Medivh telling Kadghar about opening doors and the bonds of fate and all that, which led to us going to Argus. Which seemingly was a great victory for the Old Gods, because of the One who was awakened (according to Ogmot's journal)

[DeicideUH]

It's funny that I've been thinking about making a thread much like this one, to recollect the whispers and reanalyze them.

I've been saying for a long time that the last patch will be about a War between Death and Void (more info in my signature), and it will involve Quel'thalas and Alleria's fate.

So, here's my thoughts on the many prophecies/omens we got so far:

Non-prophecies (apparently):

Flesh is his gift. He is your true creator.
He's talking about N'Zoth.

From the earth, he draws strength. Our earth. Our strength.
I think this is about Azerite.

Its surface blazes bright, masking shadows below.
I think it's the Sunwell. It's a fount of Light, but the presence of the void can corrupt it as shown in the nightborne recruitment quest. Blood elf heritage questline also shows there's something off with it, as the lantern becomes voidy once dipped into the Sunwell.

Fulfilled omens:

To find him, drown yourself in the circle of stars.
We found the Circle of Starts in the Eternal Palace and freed N'Zoth.

The king of diamonds has been made a pawn.
Explained by Azshara.

Unfulfilled prophecies:

The lord of ravens will turn the key.
I have no idea.

The boy-king serves at the master's table. Three lies will he offer you.
The Alliance is a pawn of N'Zoth. My guess is that some in the Alliance serve N'Zoth, and Anduin has been none the wiser. Maybe... the void elves?

Anduin has been telling lies, but he himself does not know it. For instance, after Crucible of Storms, when given Xal'atath, Sylvanas says "The boy-king lies to his people" about the Alliance's victory being near.

Her heart is a crater, and we have filled it.
This could be about Sylvanas, Helya or even Azeroth. Uncertain, but I guess it's Sylvanas.

Five keys to open our way. Five torches to light our path.
Like the OP said, I think the keys are artifacts, the torches are people.
One of those is the Hero with the Heart of Azeroth.
Maybe Nathanos with Xal'atath was another?

At the hour of her third death, she will usher in our coming.
Could be about Sylvanas (if we only consider her "deaths" as Undead, Alleria ("I feel like I already died twice") or Helya.

Ogmot's Journal:

Last night, Ogmot dreams of great battle. Two fleets bashin on ocean of blood.
Shadows twistin beneath da ships, risin. Risin. Ogmot so happy watching the carnage!
This foreshadowed Nazjatar. with Azshara destroying the Alliance and Horde fleets.

Today smoke rises up from da campfire. Smoke tells Ogmot good story.
Ogmot sees lady wrapped in dark swirlies. She leads herd of blind sheep.
Da sheepies follow her everplace she go. Do everthin she say. Never doubt lady.
She guide dem over tall cliff! SPLAT SPLAT SPLAT! Stupid sheepies!
Da crows get fat eatin da sheepflesh. Da lady laugh as crows eat!
This foreshadowed Sylvanas's true motives.

Dat blade has shiny eye. Always watchin us. Why you no see it?
Three lies. Da first one been told.
Bound by dat throne? No. Free. Free!
Again the lies. Apparently, Anduin had lied already in the start of BfA, then again during it (if we count Sylvanas' remark about victory not being near). So, the third lie is yet to come?

But what does "not bound by that throne" means? Is it really about Anduin?

Roused by her screams. Stirred by da whispers.
A blessin from da Masters. Now Ogmot understand!
A door. A path. Ours... Ours...
Fool! Da circle awakened us all!
I think this is foreshadowing for 8.3. "Her" screams? Maybe this is related to "her third death"? Sylvanas? Alleria?
A door opens. Somehow I can only think of the Sunwell again, which was once used as a portal already. Alleria almost corrupted it by accident. What if "her third death" means Alleria surrendering to the darkness?

N'Zoth whispers (Crucible of Storms):

Six seats at the high table. Six mouths that hunger. One will consume all others.
I have no idea.

She is not the last, but the first. Drown her and you will see.
Again, "her". "Drown her and you will see." The third death again?

The veil wanes. His crown will open the way.
"His" crown. Maybe this is also related to the boy-king's lies?

I alone can save you from what is to come.
Maybe this is related to the threat of Death brought by Sylvanas.

It grows hungrier... bolder. Alas, your eyes are closed.
Again, the threat of Death. "Your eyes are closed", "all eyes will be opened". N'Zoth is our "ally" against Death?

When the arrow finds its mark, the last fetter will fall away.
An arrow, a fetter destroyed. I can only think of Alleria losing control. Maybe Sylvanas will kill Arator and/or Turalyon?

The Light has struck a bargain with the enemy of all.
This may be related to Calia being turned undead through the Light.

The fall of night reveals her true face. She will bring only ruin.
Sylvanas, I think. Interesting that Taliesin' newest video compare Saurfang's journey to a day's cycle. "Old Soldier" happens at dawn. "Reckoning" ends at dusk. Night's coming.

He gave himself to the deep places. He gave himself to me.
I have no idea. I'd think about Deathwing, but he's dead. Wrathion? Ebonhorn? Magni? I have no idea.

Alleria's temptations:

When with Turalyon
“…can never be enough. Prove your love. Slay him and free him from the curse of the Light. Stop resisting. Give in and become one with us. It’s only a matter of time…”

Coud foreshadow Alleria’s descent into madness. Maybe something happens with Turalyon or Arator, but one of them manage to bring her back from madness. Or maybe not. Maybe she and Sylvanas end up being a free-for-all boss (one against the other, we against both), each representing a cosmic force we need to stop (Death and Void).

When meeting Vereesa
“The throne of Silvermoon is yours by right. Take it. Deliver this weak one to us, and we will grant her purpose…”

The Void wants Vereesa? Could it be foreshadowing of the fate of the high elves? This may or may not hint towards my predictions that the void taint will spread to the high elves.

When meeting Sylvanas
“This one is dangerous. She is a threat and must be ended. Beware this one, she seeks the death of all things… all possibilities. End her threat. Murder her, murder her, save yourself and murder her. Save the world and murder her.”

The Void fears Sylvanas and whatever is her master. Also, the voices say “save yourself and murder her”. Maybe because Sylvanas will kill/wound Turalyon or Arator, thus killing her at that point would prevent the dark future ahead?

When Sylvanas shows her banshee powers
“She’s a violation she serves the true enemy kill her now kill her kill her now remove her from this world and take from her what you need now now now”

Again, the void really fears Sylvanas. Maybe she’s the one who can stop N’Zoth (by killing Azeroth and impeding him from corrupting the titanic soul).

When returning to her family
“This is nothing. You should have killed her. Now it’s too late. You have sacrificed greatness for false feelings. They will leave you. You will watch as she claims them.”

Again, hinting at Turalyon’s and/or Arator’s death, caused by Sylvanas.

[Khaza-R]

Alleria's temptations:

When with Turalyon
“…can never be enough. Prove your love. Slay him and free him from the curse of the Light. Stop resisting. Give in and become one with us. It’s only a matter of time…”

Coud foreshadow Alleria’s descent into madness. Maybe something happens with Turalyon or Arator, but one of them manage to bring her back from madness. Or maybe not. Maybe she and Sylvanas end up being a free-for-all boss (one against the other, we against both), each representing a cosmic force we need to stop (Death and Void).

When meeting Vereesa
“The throne of Silvermoon is yours by right. Take it. Deliver this weak one to us, and we will grant her purpose…”

The Void wants Vereesa? Could it be foreshadowing of the fate of the high elves? This may or may not hint towards my predictions that the void taint will spread to the high elves.

When meeting Sylvanas
“This one is dangerous. She is a threat and must be ended. Beware this one, she seeks the death of all things… all possibilities. End her threat. Murder her, murder her, save yourself and murder her. Save the world and murder her.”

The Void fears Sylvanas and whatever is her master. Also, the voices say “save yourself and murder her”. Maybe because Sylvanas will kill/wound Turalyon or Arator, thus killing her at that point would prevent the dark future ahead?

When Sylvanas shows her banshee powers
“She’s a violation she serves the true enemy kill her now kill her kill her now remove her from this world and take from her what you need now now now”

Again, the void really fears Sylvanas. Maybe she’s the one who can stop N’Zoth (by killing Azeroth and impeding him from corrupting the titanic soul).

When returning to her family
“This is nothing. You should have killed her. Now it’s too late. You have sacrificed greatness for false feelings. They will leave you. You will watch as she claims them.”

Again, hinting at Turalyon’s and/or Arator’s death, caused by Sylvanas.

Also an important piece about Alleria that most people overlook :

<Alleria's eyes drift from the statue's cold stone visage down to the plaque engraved with her epitaph.>
High Exarch Turalyon: It is unsettling to look upon these memorials to our passing.
Alleria Windrunner: Indeed. Sometimes I feel that I have already died twice. Once when we were presumed lost on Draenor, and again when gripped by the shadow of the fallen naaru.
Alleria Windrunner: Perhaps death is the true legacy of the Windrunners.

High Exarch Turalyon: You're anxious. You hide it well... but I know you.
Alleria Windrunner: Like no other, my love.
High Exarch Turalyon: You don't have to go. You don't have to see her.
High Exarch Turalyon: Each of you has a path to follow. If the Light wills that those paths intersect, they will. There's no need to force the hand of fate.
Alleria Windrunner: It is time, Turalyon. I must see my homeland again with my own eyes... and hear from Sylvanas how she could ever wear the mantle of warchief.

To me it seems like Alleria is definitely going to fall. I think she is going to become the Void's champion after all the Old Gods are killed.

[Amnaught]

Both Azshara and Sylvanas have died twice.

[DeicideUH]

Both Azshara and Sylvanas have died twice.

Sylvanas has died thrice. Arthas murdered her. She killed herself in Icrecrown. That gilnean lord headshot her from behind.

But some people argue that her first death does not count, only her deaths as the Banshee Queen do.

[GreenJesus]

Both Azshara and Sylvanas have died twice.

Sykvanas died 3 times. Arthas, icecrown, godfrey

[TickTickTick]

The lord of ravens will turn the key.
I'm starting to think this is Medivh. In the recent events, we learn that Wrathion seeks a way to protect the Dragonflights from the corrupting voices of N'zoth, and he ends up in Karazhan, where Medivh helps him.
Maybe N'zoth is counting on Medivh doing something and end up as another pawn, like Magni?

I think it is Medivh and the key is the potion that we find in Karazhan. It looks like it stops the corruption, all good, but what if it's just an illusion or a time-ticking bomb? Maybe the potion is the key that had to be turned to the dragonflights to corrupt them?

The boy-king serves at the master's table. Three lies will he offer you.
This is still a mystery to me. It seems to refer to Anduin, and probably means that he's another pawn, but I don't recall anything in particular that could be considered a lie.

I think it's Wrathion, further pushing the above said by me.
To someone like Old God / Void Lord Wrathion is still young, he's probably young even to Alextraza/Kalec etc. Now, he's not referred anywhere as king, but as a Black Prince. But it was a title that he took when Deathwing, his father, was still alive. After Deathwing's death, Wrathion could practically become the Black King. Yes, I know there's albo Ebonhorn, but it's not like Wrathion is a literall prince/king, it's just a menancing title.
I still think that Wrathion wasnt successfully cleaned of corruption back in Badlands, even if he thinks he was. So he might be serving without realizing. Remember, he was the mastermind behind freeing Garrosh. If it didn't happen, there would be no Gul'dan, no Legion invasion, no Sargeras sword, no Azerite, no Heart - meaning N'zoth wouldnt be freed.
First lie could be about the potion protecting from corruption, but maybe it was something from back in MoP. Something from his philosophies during legendary cloak questline, or maybe the message he got after he ate the heart of Lei Shen.

Her heart is a crater, and we have filled it. First time we heard this we though it meant Azeroth. Now I'm pretty sure it meant Sylvannas. Since her death, over the years, she sees how all she loved is lost: her homeland, Silvermoon; her sisters' love; her hope to savethe Forsaken from extintion.
Seems like she found something that led her to the Old Gods and some promises we still don't know.

Still think it's Azeroth. I think Nyalotha is precisely where Azeroth's "true heart" is, and the Old Gods successfully got there many years ago and that's how Nyalotha came to be. It could be the greatest font of power on the planet and a fine feast for the old gods at a time. Also remember that Argus titan soul was able to resurrect demons. Maybe Azeroth's titan soul which is in Nyalotha is able to resurrect old god minions, thats why all of them travel there after death and thats why there are always more and more after we've killed so many?

Five keys to open our way. Five torches to light our path.
Xal'atath refers to us as "the Opener... the Bringer of Truths... the Torch That Lights the Way!".
Opener: as in we use the Heart of Azeroth (the key) to open N'zoth's prison.
Bringer of Truths: as in freeing N'zoth we lead to Sylvannas revealing the truth, that she plotted with Azshara to start a war and use us all to free N'zoth.
The torches are not things like we though. They are people.

Well, it was us who collected the Pillars of Creation. It was us who placed them in the Tomb. If it wasnt for this, then again - we wouldnt end up on KJ's ship, the portal wouldnt be opened, Sargeras wouldnt have the way to get to Azeroth, no sword, no wound, no Azerite, no Heart - N'zoth cant get freed.
Find the five pillars of creation and placing them in the Tomb set in motion the future events that otherwise wouldnt be possible to happen.

Its surface blazes bright, masking shadows below.
X'era, or maybe another naaru we'd meet in the future.

Probably just depths of Azeroth (Nyalotha?), there's so much shit we still dont know about the undergrounds and deep places.

[GreenJesus]

Sylvanas has died thrice. Arthas murdered her. She killed herself in Icrecrown. That gilnean lord headshot her from behind.

But some people argue that her first death does not count, only her deaths as the Banshee Queen do.

Why would her first death not count?? Because blizzard forgot to count and went "oh shit.. just kidding guys! That one doesnt Count!"