As the title states, I think a speculation thread would be a fun way to pass the time between now and blizzcons "What's Next".
Educated speculation would probably be the most productive to conversation, nothing too farfetched.
I'll start:
If the Burning Legion are in fact the focus of the next Expansion as speculated, wouldn't it be cool if the next stage of raiding would be the possibility of mixed alliance and horde raid groups? Banding together to fight a common enemy has always been hinted at, lets make it an actuality!