But what will the setting of her expansion be? Vashj'ir's mechanics weren't too popular so we can probably eliminate an entire expansion taking place underwater. The Lost Islands may sound like good setting but there's a good chance the Cataclysm destroyed them all (the troll prophet in Kun Lai says that Zandalar Island is destroyed).
So what if Azshara, combined with the power of N'Zoth and the subdued Neptulon, rose a large chunk of the ocean floor and have it float above the sea? We've ran out of room for continents unless we get another Pandaria (It's always been there in lore, just hidden) so I think it would interesting to see something like Outland but with a more "natural" feel to it. Her plan? Revenge, conquest, unleashing N'Zoth, etc. Maybe another go at the Emerald Dream since Xavius was defeated (6.2 content patch!).
We get the best of both worlds here. We get the Naga and Elf lore for the WC III fans and we get a lot of original land that has a tons of room for creativity. For the two faction cities, the Horde can get a miniature Kezan 2.0 while the Alliance gets a Night Elf version of a miniature Dalaran thanks to Jaina kicking the Sunreavers out.
Similar to how the majority of Northrend is covered in snow yet all zones look different, not every zone in this new continent has to look the same:
Nazjatar City (The entire zone is the gigantic city)
Forest zone (Former underwater forest created for Azshara)
Dried up muddy zone of geysers (where a Well of Eternity is being made using that last vial)
Corrupted reef wasteland zone for N'Zoth and his lair
Canyon zone for both Faction cities
Salt flat with mountains (shout outs to the old Shimmering Flats)
Volcanic zone covered in ash since there was previously an underwater Volcano
Drained reef zone with crystals (Think Deepholm but outdoors and prettier)