Replaying the BfA quests, they actually had some really cool zones and lore in Kul Tiras. I am more and more convinced that Nyalotha was going to be in the Shadowlands expansion and then they changed development completely at some point in BfA before 8.3 to make the version of Shadowlands we got.
It didn't help that probably the systems and combat in BfA were so bad. Some of the negative feedback about the faction story probably made them want to rush to tie up the Old Gods narrative prematurely and try to wipe the slate clean.
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Who knows. We have no idea what the plot will be. The immediate threats right now are Iridikron and the Harbinger (who is most likely Xal). Why would they want to go to Avaloren? The plot suggests they want a way to capture the World Soul. Given that the world soul is LITERALLY inside the planet (we see it in Argus) that would point to an underground expansion, NOT Avaloren. Maybe as per my suggestions on what could possibly happen there, Avaloren has some abandoned Titan Facility (a Forge) that could be used to achieve that (my idea was that the Titans built the Forge of Awakening there, a facility meant to midwife the World Soul).
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I mean 10.2 does add the Elun'ahir and Erinethria's brood story. The latter absolutely is tied to Avaloren (conservation of detail and all). The former possibly could also be there (it could also tie to an underground expansion with Elun'ahir being the source of an underground forest zone).

@Nymrohd I really like this conversation. So, let's say we go underground, what should that look like?
Avalon may have been based on a towering hill which looked like an island when mists rolled in. It may also work as some kind of island that is hidden for periods of time.
I think it'd be cool if there was a central high island and they put tides into the game so that surrounding zones would sometimes by underwater, sometimes by dry land.
1) Arthas specifically didn't do what the Jailer wanted (spreading death's influence across the mortal plane) The entire Lich King idea failed.
2) The only thing that changed in this storyline was that the nathrezim had their own agenda in mind when the Legion decided to use undead to weaken the planet.
So, let us focus in DF for a bit. Can we all agree that Uldaz is coming within DF? Details:
- Uldaz is mentioned in The Infinite Hand, a drop from Dawn of the Infinite.
- Dawn of the Infinite is going to be relevant in 10.2 as a Mythic + dungeon.
- Dawn of the Infinite will not be in another Mythic+ season for years after 10.2 (DF's seasons have not had any SL dungeon).
First conclusion: Uldaz has to come within DF. Otherwise, The Infinite Hand will not have a relevant IL for Uldaz.
- WoW's expansions have never received more than one megadungeon. So Uldaz will not be a megadungeon, as we already have Dawn of the Infinite.
Second conclusion: Uldaz will be a raid or a zone. I am putting my money on 10.3's raid.
- Odyn sent three expeditions to Avaloren when Kalimdor was still one continent. When he did this, he was in Ulduar acting as Prime Designate of the Titans.
- The remnants of the last expedition that Odyn sent came back to the shores of Kalimdor.
Third conclusion: Avaloren is not far from Northrend. Probably to the northeast, between Northrend and the Dragon Isles.
- Avaloren's Heretics resisted three Keepers' incursions. It is unlikely that if Avaloren was a continent, would have defenses in all its shores. The Keepers would have found a way to get in if that were to be the case, but they did not.
- Avaloren was introduced in DF. We do not know anything about it. It has never been the case that Blizzard introduced a new zone just to have the next expansion centered around it.
- 11.0 will not be Avaloren. A world revamp is coming and chances are that it will span several expansions. There is no room for Avaloren for many years to come as a full continent.
- There have been several cases of unknown zones introduced in an expansion that were later introduced as patches of the same expansion: Isle of Thunder - Timeless Isle - Mechagon - Zereth Mortis.
Fourth conclusion: Avaloren is not a continent but an island. It will be 10.3 zone, and it will have Uldaz as a raid.
That's it. I cannot fathom why we will go to Avaloren. There could be many reasons. I think that Iridikron would go there to seek the support of the Heretics now that he does not have an army. He would want to reach Azeroth and Uldaz might be the key to it. We might defeat him but he would fuck something up that would lead us to 11.0, whatever that might be.
Of course I will be completely wrong, but I would really like to get something like that.
Do not take life too seriously. You will never get out of it alive.
Not only that, but show a cool fight scene between two badass looking dudes, and then show cool features like legion and the expansion would be popular reused zone assets or not. Regular players don't care about that stuff.
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I love your positivity.
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Yeah this"filler" education
Expansion sounds better than half the other wow expansions to me.

https://twitter.com/MrGMYT/status/1718413300071809254
Hmmmmm...
I remember one of the leaks mentioning dynamic weather.
It's unlikely 10.3 exists and your foundational piece of evidence is flawed: Strom'kar had a flavor effect that worked in a bunch of irrelevant old locations. There's no reason to assume the reverse can't also be true, with a weapon that's no longer relevant having an flavor effect that works in a new location.
My idea has consistently been Hollow World. We have a central zone at the center of the planet with titan facilities that surround the world soul and then we have existing underground areas that were never properly added in WoW used as zones that can lead to the center of the planet; think Azjol'Nerub, Hyjal Barrows, Molten Core, a zone based on Elun'ahir, possibly a zone that is literally inside the corpse of an old god burrowing deep like C'thun.
On Avaloren and what could be there my main idea would be, what existed before the Black Empire. We know elementals were there and we know there was some mortal race cause the Aqir were clearly enslaving and sacrificing something.
I think pure elementals would be fucking boring. But several of the elemental planes have other creatures attached to them. Fire has salamanders and the phoenix, Air has Djinn. Earth was sadly the one with the least variation (since they just used Earthen and Troggs instead of adding something completely new, plus earthy variations of existing creatures like the Gyreworms and Shale Spiders). But I am sure we could come up with something and heck, we could even use existing creatures that have no clear origin; the Kul Tiran sirens could be either Water or Air elemental descended.
As for the mortal race, whatever existed before trolls. Maybe a proto troll that followed a completely different path of evolution.
Beyond that, if Elun'ahir is there then there is a link to Life and thus I expect Wild Gods.