Blizzard,huh...
Dosent necessaraly mean it's coming out anytime soon.
I will believe it when i see it or better yet,playing it.
Blizzard said that the development schedule for it was pretty aggressive. They have the engine for it already (since they intend to make it seamless with Wings of Liberty in terms of Multi-player). May not be out soon soon, but it's not as far away as you think.
According to them, it's supposed to add additional units to the Multi-player matches as well (similar to Brood War expansion did to the original StarCraft).