That actually sounds really freakin sweet. I would totally buy that game (the pre-order should come with a free sweet-yahtzee hat) and play the hell out of it, oh and yahtzee should to the voice over for the tutorial, just to fuck with people, can you imagine yathzee explaining the control scheme in his lightning-fat-thick-acscented voice? It'd be funny as hell watching people try to catch what he's saying.
Though when you said guitar hero rock opera, i was thinking like, have like little cutscene's the bring you through the basic story of a movie (like tenacious D and the pic of destiny) and then you play the songs chronologicly, each movie would represent a teir, so it's like watching a shortened version of the movie, but you get to play all the songs. You could do movies like tenacious D,....um... A Hard Days Night, Repo the genetic opera, HELP! Across the universe..........The Producers? Okay obviously you'd have to find some good music movies to fill it in, but the concept...well it makes sence
Eh your ideas better anyways, mines just a thought.