A couple of months ago, Blizzard revealed its entirely new project other than Starcraft II and the great MMORPG WOW, but declined to name it. But, it seems like cat is out of bag as darkspirefilms.com has revealed company's new project named Project Hydra. However, the site doubts that this is a pseudonym used for Diablo III by the developer.

I think, basis of assertion given by (blogger) mate is statement coming from Frank Pearce (Senior VP of Blizzard), who says 'the new project has nothing to do with WOW and Starcraft II' i.e. he don't have mentioned 'Diablo' while talking undergoing project.
As nothing is confirmed yet, hence to take it for real would be a great idiocy and obviously, the recent speculation has burdened me with some more research work.
We will post an update as any new surfaces. Stay tuned...
Via: Darkspirefilms