Well, if the news of Blizzard announcing a new title next month isn't enough, it looks like they're also working on a next-gen MMO.
As you can see by their Employment Opportunities page, they're looking to bring on multiple people for a "Next-Gen MMO."
The three openings are for Lead Engine Programmer, Lead Tools Programmer, and Lead Technical Artist, so it's safe to say that this MMO is in the very early design stages.
That said, could this new product announcement next month, and this MMO be one in the same? Only time will tell, but this summer should be an interesting one, to say the least.