For the most part, I agree with the general sentiments in this thread (this is abuse of github), but the ability to change already distributed music is a great idea.

It would be really cool to open your music software and be able to listen to the artist's newest iteration of a song (like while it's being written or polished during studio time). You could follow the entire evolution of an album from birth to release. Or you could browse the various remixes and changes that others create. It would be a world wide jam that could extend for weeks or months that anyone could enjoy as either an audience member or a participant.