Besides confirming that they indeed have absolutely nothing to do with Guitar Hero 3 and the future of that franchise, Harmonix told Gamasutra that they are instead working on something bigger and better. From Harmonix producer Daniel Sussman:
“We are instead working on a different music game project, one that is a bigger and more ambitious endeavor than we felt we could pursue within the bounds of the Guitar Hero franchise.”
Greater than Guitar Hero and the entire franchise? That’s a tall order. Wanna take bets on a Band Hero-type game in the works for Harmonix? You know, every single instrument would be represented. Anyone got a better guess than that?