Alright before everyone starts to think that there's going to be yet another wave of plastic instruments to deal with, this addition to the series does away with the instruments in favor of the controller. It will be a digitally released title on the XBOX Live Arcade, and PlayStation Network. The name of the game is Rock Band Blitz. Now the real cool thing about this game is that there will be new tracks that can be played in Rock Band 3, and any songs saved on your console will be accessible for this title.
Now from what I can tell there's no finite release date, but I would assume its coming sooner than later. So if you're still in the Rock Band crowd, this might be a game that you keep a close eye on. I'm sure that Harmonix will have plenty to say about this game as time goes on.