Destructoid interviewed Frank Pearce, executive producer on World of Warcraft, at the VGAs, and surprisingly Pearce agreed to talk (very briefly) on their project called Titan. He confirmed that it's Blizzard's next-gen MMO in the works, and at the moment they're recruiting to get the best available people in the industry for it.
"The media is not meant to know anything about [Titan]. It's our next gen MMO and we've only started talking about it in a limited fashion because we want to leverage the fact that we're working on something like that for the purpose of recruiting –— getting some of the best talent in the industry on that."
Blizzard are notorious for not talking about unreleased projects, let alone unannounced stuff. So that they're even willing to mention it is pretty exciting, and maybe we'll see more solid information about Titan soon. Titan is obviously only a codename, and is very likely to not be the actual title. So are we looking at a new IP? World of Starcraft? World of Warcraft 2?