So you come along some rumours while browsing the internet, and this time: WOW. If this turns out to be true, I am a very happy gamer indeed!
So let's start by looking through some of the given facts and see if it looks realistic. To start off, it would be a multiplatform game for the PC, Playstation 3 and Xbox 360, with a DS version in production. This doesn't seem realistic for two reasons though: Blizzard isn't known for bringing out games to platforms, and the fact that Blizzard takes their time creating games and the DS is at the end of his lifecycle with 3DS around the corner.
But this doesn't mean it isn't reliable, because Activision works together with Blizzard now. Activision could have pushed Blizzard for a multiconsole release, and maybe they make shorter work of the DS version or transfer the development to the 3DS.
It would work with the same engine as Starcraft II and it should finally have a team for it since the game is out. Thrall is 'currently' in it and they are considering a episodic campaign. It is currently planned to release in Q4 2010. Sounds pretty believable to me...
The source of these sudden rumours is vgtribune, and they received this information from a 'fairly trusted source'. I don't know if that sounds trustworthy, but nonetheless a fun rumour.