This is my own personal take on how the next expansion could look like. This is NOT a leak, be it a fake or real one.
In my view, the next expansion will be centered on Azeroth, but will have cosmic forces 'invading' later on to subjugate the planet.
World of Warcraft: A New Dawn
At the end of Shadowlands after the defeat of the Jailer, we learn from the First Ones archives that Azeroth is truly special, created with an affinity to all the different cosmic forces, but should one of them take control of her, she would completely align with that force, destroying the balance and giving that dominating force control over the whole universe.
As the true defenders of Azeroth, we need all the forces we can muster as more invasions are surely to come, which leads to us needing to re-imbue the dragonflights with their powers.
Wrathion, who finally has found the Dragon Isles, leads us there.
10.0
Launch continent and leveling zones will be the Dragon Isles; consisting of 6 zones, one for each dragonflight (green, red, bronze, blue & black) and one small Crystalsong Forest-like zone dedicated to the overarching Wyrmrest Accord reformed.
During questing we help the Green Dragonflight in the ascension of Merithra to their next aspect, as well as finally clearing the last remnants of the Nightmare out of the Rift of Aln during the ending-scenario.
The Red Dragonflight needs to come to terms with all of their offspring gone from the purging of their Sanctum at the hands of the Deathknights during Legion. The discovered Twilight eggs beneath Grim Batol will be essential and Alexstrasza in the end takes her warped 'children' back under her wings to give her dragonflight a future.
Wrathion discovers a small sect of black dragons in their respective zone and struggles to exert dominance and have them accept him as their new aspect. All his sassy-ness can't help him and he is truly forced to reflect on his actions of purging his own flight during Cataclysm and beyond.
The Blue Dragonflight has to contend with the remaining Twilight Cultists in the area, who draw upon the unearthed leylines and driven mad by the overwhelming arcane energies still think their Void masters will return; summoning in Void creatures in the fallen Titan facility of Uldorus.
The Bronze Dragonflight finds a barren wasteland instead of a place of rebirth with no hope of them recovering their lost powers, which finally leads to the fall of many and their transformation into the Infinite, including Nozdormu becoming Murozond.
Each of the 5 zones would have at least one dungeon at launch, with one additional dungeon in the shared zone.
The first raid of the expansion and concluding the starting experience will center around the Infinites with Murozond as the final boss, who rips holes into time and space, showing us a void-infested as well as a crystallized light-forged Azeroth.
10.1
The first patch extends and then wraps up the other storylines of 10.0, delving into the underground of the Isles via the entrance in Uldorus, revealing a new zone of titanic construction that is completely Void-infested. As it reaches under every other zone, it is discovered that the true power of the zones that gives the dragonflights their powers back are of titanic origin. The pillar powering the Bronze is already destroyed and its power sucked into a huge void portal, which explains why their powersource on the surface wasn't available.
The raid of this patch deals with this exact problem, closing the portal and driving back the Voidlord that is trying to manifest through it.
10.2
In the cinematic introducing this patch the Dark Portal will suddenly change color, turning golden and emitting melodic sounds. Shortly after Yrel arrives, accompanied by the new Prime Naaru and her Lightforged Army from AU Draenor.
The patch will deal with the revamped Western & Eastern Plaguelands, where the Scarlet Crusade has re-emerged after the fall of Lordaeron and its abandonment by the Forsaken. With the death of Tirion Fordring and the reformation of the Paladin Order Hall during Legion, the splintered remnants of the Argent Crusade have joined forces with the Scarlets, taking up residence in Hearthglen, Andorhal & rebuilding the farmlands into bastions of the Light, as well as cleansing the EPL and re-taking Stratholme as their capital.
The quest campaigns will be completely different for the Horde and the Alliance here.
Where the Horde and especially the Forsaken under the banner of Calia Menethil want to reclaim their former homeland, cleansing Tirisfal and drive the Scarlets out of their lands once and for all. The Alliance, still under command of the now High King Turalyon, wants to bring the newly-emerged faction of the Light into its own ranks instead of battling another enemy.
Both sides end in a victory, as the Horde is able to claim dominance over the Western Plaguelands and de-toxify Tirisfal. Whereas Turalyon and Yrel's Lightforged Army take over Stratholme, Yrel usurping their leadership and either lightforging every single one of them or outright killing those who refuse.
It escalates in the last chapter of the campaign when Yrel tries to lightforge Arathor, Alleria trying to save him but accidentally killing her own son.
This drives Alleria over the edge and she succumbs to the Void. Turalyon distances himself from his wife and throws her into a specially-crafted prison on the Vindicaar, which now hovers over Stratholme as well.
All this leads into the raid of this patch, where both sides attack and try to cleanse Stratholme of their new masters, including a fight against Turalyon to rescue Alleria, and ending in a confrontation with Yrel bolstered by the new Prime Naaru. In the end shortly before she is defeated, Yrel gives the command to make the Vindicaar flight-ready, and with the help of the Prime Naaru the spaceship with all heroes onboard transports through a giant light-infused portal to an unknown realm.
10.3
The heroes of Azeroth are transported to the plane of Light, where they are imprisoned and have to fight back against an unbeatable, limitless force. They are not outright killed, however, but it turns out they are rather tested, if they can retain their own will after being lightforged and to be made into champions of the Light to wage war against the True Void. The Light still seeks a replacement for Illidan, the One who should have brought the endless war to an end.
The initiation and last rites and tests are the first half of the final raid, when the Void attacks the Light itself using the void-touched Alleria as a beacon, and in the ensuing chaos the heroes of Azeroth need to fight off everything and everyone.
In the end only with the help of Alleria they escape through a Void portal that leads back to Azeroth, but one that they don't recognize - An Azeroth that is the true rebirth of the Black Empire. Which then leads into the next expansion.