Absolutely no way of guessing until we get some indication of what it'll be.
It is pretty full. But the best idea I've heard for a 'Great Seas/Azshara' expansion would be Azshara and her naga causing portions of ancient kalimdor that sank to the bottom of the ocean during the Sundering to rise up, forming a new island-continent centered around the Maelstrom. They would form the bulk of the new zones, with existing islands like Kezan and Kul Tiras included as faction bases, extra zones, etc.
Could be any number of zones underground. And obviously the Dream would be in an alternate plane.
But there is a stable portal there that leads right to Azeroth.The Burning Legio has no reason to be interested in Outland. Its a barren world striped of resources, and according to Cata and MoP, just about everyone migrated through the portal to Azeroth; very few people remain there.
That is also possible. WoD hints at an entire continent of ogre empires that existed in the past - fragments of it may have survived to form other floating land-masses in modern Outland as well.I'm thinking additional continents on Draenor, other worlds, or alternate planes.
For an expansion set in other planes, we could always go and explore more of the elemental planes - we only see bits of Firelands, Skywall, and Abyssal Maw, and there could be other regions in Deepholm and the others we never got to see. I'd love to see what's happened to Firelands after Ragnaros' death and Deepholm after its infestation with the Curse of Flesh.
Well, Azeroth isn't really full. I can name a dozern other MMOs and fantasy settings that have 6+ continents and you can easily keep track of them all.
Then just wield an iris onto the portal like Stargate, better yet just dismantle the whole thing.
Or-gre kingdom? Exactly what I was talking bout!
As much as I don't think the game needs any more classes, races or professions, I'm sure they're going to dream one up and try to fit it in somehow.