A PaRappa PSN title makes sense to me, I doubt it would fly off the shelves as a full-price release. Vib Ribbon might be nice to mess about with for those who stream Spotify (etc) through their consoles (assuming you can do this).
I like this song generation games, but sometimes the link between the song and the level is kind of hard to see. The worst example of this was a space invaders game on ipod touch.