I don't see this happening. Guitar Hero is just a game. Sure it's quite popular, but with the popularity of the iPod, making something that competes with iTunes is quite difficult.

You'd sort of expect a guitar hero type game for the iPhone sometime soon. For extra points it'd analyse your mp3 library and write the guitar part itself.

Guitar hero looks like fun, and a good game. It's just a shame all the songs it comes with are godawful :(

Rock Band is where it's at.