News from Eurogamer.net has appeared that quotes Dustin Browder, lead designer of StarCraft II commenting on the release of Heart of the Swarm.
I don't think you'll be playing it this year. That seems very unlikely to me. But we're pounding away on it as fast as we possibly can.
The question was posed to Dustin Browder at the Interactive Arts and Science Awards.
Looking at the wording, "I don't think you'll be playing it this year" could also include BlizzCon, hinting that a playable demo won't be available.
Eurogamer.net - Heart of the Swarm "unlikely" for 2011