The only positive I can see in this idea is who the characters might be who you can use...
I think this would be boring to be honest. I enjoy playing worship music on a real guitar, but it's not exactly guitar driven music. Not a lot of licks, riffs and solo's to make a game interesting. Just a bunch of Edge inspired textural stuff. We were joking around here that the controller should just have three buttons: one for G, one for C and one for D and then you just strum different rythms
Of course call me old (I'm not really), but I got really bored with regular Guitar Hero and Rock Band... It was fun for about 10 minutes and then I thought "hey, I have a real guitar right there what am I doing with this toy!?" I'd much rather spend my time playing a real instrument than playing a game pretending I'm playing an instrument I already play