It was announced by X-Play earlier this evening that Harmonix next game will be titled Rock Band Blitz, an Arcade title that looks similar to Rock Band Unplugged for the PSP and Lego Rock Band for the Nintendo DS. The title switches control of the game from use of a plastic guitar to your normal controller to hit notes on the musical highway, allowing you to swap between different instrumental tracks.
One big benefit of the title would be the inclusion of all your previous Rock Band DLC, which will be able to play in the game, along with 25 new tracks that can be ported over to Rock Band 3, which mean you have the potential to play over 3,500 songs!