I honestly hope for a revamped kalimdor/EK, overtaken by naga/old god influences (that could be easily removed after that expansion instead of still scarring the world for 6 years and 3 expansions later like Cata)
But also updated overall to fit the post-legion timeline, no more garrosh/deathwing quests in pre-cata zones.
Cleansed Plaguelands (holy influence extended from the pala class hall) + connected landmass to ghostlands, added flying, updated Silvermoon.
Azuremyst isles added to kalimdor map allowing direct boat to stormwind/flight connection to darkshore, Isles cleaned up, most exodar debris removed, blood elves replaced by some other quests.
Loch Modan Dam repaired
At least a bridge between north and south barrens.
Zone level ranges more fluid once again + scaling 1-60, zone objectives.
When expansion is unlocked , relevant quest zones in Kalimdor/EK existing zones become available at high level.
Low level wont encounter max level mobs and will have altered quests.
World quests could be split per faction/continent, so each faction doesn't compete for mobs unless it's a world boss, and is closer to the faction main capitals.
Added islands/sea regions for more naga/pirate/undersea/trolls content:
Zul'dare
Kul'tiras
Plunder isle.
Tel'Abim
Zandalar
After that a Void expansion, which uses Tempest Keep as main city and travel hub, the layout definately caters to a neutral district, and a horde/alliance seperate district.
Updates in netherstorm as a staging area, Old raid can still stay there with some bronze dragon npc trick.