Sabbath could work -- interesting suggestion. There's some interesting stuff there with Iommi cutting his fingertips off and then re-learning how to play, and then the tensions between Iommi and Ozzy. Maybe cover an onstage incident with a bat. Ozzy gets fired. And the solo-Ozzy tragedy of Randy Rhoads.
Not a huge fan of the music, but there's quite a lot of dramatic meat there on the bone.
I also think that a Queen II film would work. There's enough great music post-Live Aid to sustain it. And really the truly deep stuff kicks in when the band had to deal with what Freddie was going through.