I thought it was World of World of Warcraft?? ;P

I would guess it will be something that will not damage their current WoW playerbase too much.

Something cyberpunk, gothic or sci-fi would fit that bill IMO...of course so would Hello Kitty. Of course, it could even be some type of sports MMO, that would probably make them some good coin. Who knows. I just don't think it will be another medieval-Tolkien-type fantasy MMO. Perhaps they could get away with something similar like vikings, pirates, martial arts or WWI or WWII type warfare.

I'd also guess that patch 3.1 may have been the testing ground for some of the concepts.

I am hoping it's Starcraft....