Well, we fighted Deathwing who got maddened by N'Zoth, which is responsible for the Emerald Nightmare.
Also, Ysera, the guardian of the Emerald Dream lost her powers along with the other aspects.
So ... isn't the Emerald Dream more vulnerable to the Emerald Nightmare since Ysera can't protect it ? Here is my expectations, on the next (or after the next) expansion, we will probably have to cure the Emerald Dream from the Emerald Nightmare and finally kill N'Zoth, we'll have to replace Ysera and mortals will become the new guardians of the Emerald Dream.
Since Azshara and Xavius are N'Zoth's minions, we'll probably have to fight them in early and mid tiers as final bosses.
Plus, we'll maybe have to fight Neptulon since he's the most pernicious of all the elemental lord, but he has been weakened since the Naga stole his trident.
Azshara = Naga.
Neptulon's Trident = New legendary weapon ? (This weapon have the power to controle the ocean).
I imaginated that we could have to bring the trident back to Neptulon by killing Azshara, starting a long quest ending up by fighting Neptulon who betrayed you (Why ? Cause he's evil lulz), in order to get his trident and use it for yourself.