Here is some juicy info on 8.3 and the next expansion.
I can't say how much of this is 100% accurate. This is all stuff I've been able to patch together from the information I got.
About the leaked map:
>It appears to be a WIP map, one of many that were presented during a layout pitch meeting about 1-2 years ago. The logo is a probably placeholder/suggestion made by the presenter for that particular pitch. It's not unusual for the developers to spice things up. The real logo is always finalized shortly before the actual announcement. Many of the 'hub' names are also placeholders, but the main zone names were pre-determined.
>The map is actually very representative of the final design of Shadowlands. So far, every zone except Ny'kaithos is represented in the development version of 9.0.
>Because the photo of the Shadowlands map was taken so long ago, probably nobody can recall who exactly attended the meeting, and certainly nobody remembers who was sitting where.
>Shadowlands isn't all dark and gloomy. The concept art for Xiros and Darkfront is very colorful. The Riftlands feels more like a psychedelic Outland.
>The blood trolls in Morbara are not our enemies. They are being tortured for their failure to worship Hakkar in life. The zone is nothing like Nazmir, so troll fatigue is not a concern.
>Mueh'zala is present in Morbara, but is weak and afraid of Hakkar. He is shapeless because Hakkar has destroyed his corporeal form.
>Ny'alotha lies within a pocket universe. That's why it says 'transit'. However, this does not change the fact that the Shadowlands and Ny'alotha are now connected. The island of Ny'kaithos is the Old Gods' attempt to build a permanent foothold within the Shadowlands, but this plan is foiled by us in the dungeon there.
Patch 8.3:
>The last boss of BfA was indeed shown in the Azshara defeat cinematic, but it's more metaphorical than people realize. The last boss is us: Alliance & Horde, as indicated by the last shot of Jaina and Lor'themar. Azshara and N'Zoth are both bosses in the next expansion. We won't be facing them again (at least physically) in BfA.
>Sylvanas will prepare a strike against Thunder Bluff, tricking both the Alliance and Horde into defending it. During this distraction, she will invade and conquer Stormwind. The latter will be explained through a comic released in October.
>It has always been the plan to finish the expansion with a raid-version of Stormwind. Therefore, patch 8.3 includes a 10-boss raid within Elwynn and the city itself, along with a complementary, all-new 40-player battleground.
>In the raid, Horde and Alliance players fight alongside important lore characters and leaders from both factions.
>Sylvanas has already taken Stormwind at this point. The raid is about defeating Sylvanas and reclaiming Stormwind.
>The first boss is a sort of caravan-escort scenario. An azerite-powered battering ram made by goblins & gnomes will start at Goldshire and travel slowly towards the gates of Stormwind. Waves of adds will attack the ram in an attempt to destroy it.
>The second boss is Old God aligned and has enslaved city guards and other famous Stormwind NPCs (such as Topper McNabb).
>Another notable boss is Anduin. Halfway through the raid, he will succumb to the whispers of N'Zoth. We must fight him until he returns to his former self. Wrathion makes a special appearance during this fight. N'Zoth is trying very hard to keep us from reaching Sylvanas.
>The 8th boss is Nathanos. This encounter takes place in Cathedral Square. Tyrande decapitates him at the end of the fight.
>The penultimate boss is Sylvanas. She awaits us in Stormwind Harbor. MASSIVE SPOILERS NOW. BE WARNED!
>Sylvanas is the first of two encounters that comprise the grand finale of BfA. Alliance and Horde will fight side by side against Sylvanas until Bolvar eventually appears and starts killing Horde leaders – first to go is Lor'themar. Bolvar will then side with Taelia and the Alliance. Sylvanas will shoot Genn in response, prompting the intermission.
>During the intermission, all of the Horde leaders will rejoin Sylvanas. Genn dies, and Anduin and Jaina declare war on the Horde. The final fight begins.
>The final boss is 'The Horde' or 'The Alliance'. This encounter is cosmetically unique to each faction, but strategically identical. Horde will win once Anduin is dead, and Alliance will win once Sylvanas is dead.
>The encounter has been designed to have your faction's leaders die one by one as the opposing faction's health ticks down. The players will all die as well (like the Arthas fight), with Anduin and Sylvanas being the last ones standing.
>A cinematic will play once the encounter is over. Anduin will end up killing Sylvanas or vice versa (depending on your faction), only to die of his/her wounds. Ultimately, everyone will be dead, and the harbor will be silent. Characters will then wake up in the Shadowlands, and a ghostly fleet of Helya's ships awaits us in the death version of Stormwind Harbor. With Nathanos by her side, Sylvanas declares that we're now strong enough to face the true battle for Azeroth.
>A short teaser-cinematic starring Gallywix and Mekkatorque will be shown at Blizzcon in November. Gallywix, who fled from the fight in Stormwind, will eventually find King Mekkatorque's escape pod and awaken him from suspended animation. Together they figure out what happened and construct a device that will allow us to enter and leave the Shadowlands at will. Their cooperation lays the groundwork for the new Tinker class. The device is rumored to be the 'Dalaran Hearthstone' of 9.0, given to you at the end of the introductory questline. It works like monks' Transcendence ability.
>Calia is the interim Forsaken faction leader during the raid.
>BfA's patch release schedule feels slower because the plan is to lead into 9.0 much quicker than ever before after the release of 8.3.
>You can have a physical form in the Shadowlands if you are brought there artificially, either by its denizens (such as spirit healers) or by means of 'dimensional' technology.
>The Dragon Isles, the Shadowlands and the Old Gods have a much deeper connection than one would think. This is explained by lots of quests and dungeons, but I don't know any specifics besides the shrines in Dragonblight and on the Dragon Isles being connected to the Shadowlands, somehow. This connection will also play a major role and be explored in the patches going forward. The Curse of Flesh also plays a role in this.