Someone posted a video of the band playing the horrific cover of "Juke Box Hero" after which the band talked about how they had to break down their SONGS into "stems" for use in the game.
To me, this means that MASTERS are coming in the near future. Why would the band send Harmonix stems of their songs if it were only for a cover? Plus, they said "songs."
Not my favorite band, but a master track of Juke Box Hero, among others, would be pretty fun to play.