At last night's DICE 2011 Keynote, Blizzard's Mike Morhaime talked a bit about Blizzard's upcoming, unannounced game.
"We have some of our most experienced MMO developers, people who spent years on the World of Warcraft team, working on this project. We're really trying to leverage all of the lessons that we learned throughout the years, some of which we were able to in World of Warcraft, and other that maybe because of some of the design decisions that we've made we just can't address.
"We're basically trying to take a step back with all of that knowledge, and do something that's completely new and fresh. We're not trying to make a WoW sequel, so we actually envision these two games coexisting in the future. We really value the social experience of being able to play with your friends, make new friends in the game, and the whole guild experience. Games are more fun when you're experiencing them with other people, whether it's competitively or cooperatively.
"With Cataclysm, we did something pretty dramatic. We went back and redid the entire old world, we redid the quests. But we didn't actually change the game itself. We think there's a lot more that we can do within the context of World of Warcraft, but sometimes to break the mold you have to start over."
So, he obviously didn't drop a bomb and tell us the title and concept of their next MMO, but it sounds like they don't think they'll be poaching from their existing Warcraft audience with these games coexisting, so it seems like a logical conclusion to assume they'll be leaving the traditional sword and sorcery route of WoW and Diablo.