As a follow-up to our speculative post regarding the future of Guitar Hero development, Harmonix has cleared up the whole mess in an interview with Gamasutra. We'll hit you with the good news first: Harmonix is in fact working on a brand-new music title. The (possibly) bad news being that they will not be involved with Guitar Hero III, leaving that title in the hands of, presumably, Neversoft.
Regarding the new project, Harmonix producer Daniel Sussman took time away from reading the blogs of his favorite Laguna Beach cast members to say it's "a bigger and more ambitious endeavor than we felt we could pursue within the bounds of the Guitar Hero franchise." Though he could have just been talking about the new Fall Out Boy album (they're still hot with the kids, right?), we're excited all the same for whatever the future may hold for the MTV-owned developer.