I will give full credit to the first game but how are Rock Band 2 or The Beatles: Rock Band innovation or revolutionary?
I shouldn't be so sarcastic and cynical though. Guitar Hero is responsible for my disinterest in these games. It kind of sucks for Rock Band because they've been reasonably good at not overexposing the franchise. The genre will die because of Activision and this series will be taken down with it.
I don't have any Rock Band games because they dropped the ball with the first game's Wii release so I went with Guitar Hero instead. And there's too much crossover between the two series to really embrace both. I really just want a standardized "band game" where I can pick and choose whatever song I like. This is never going to happen because the genre is overexposed. Even if the two companies wanted to join forces, no one cares anymore.
Keyboards would make sense as the obvious next step though. Where else do you go? Sax? There aren't enough songs that really make use of that instrument. There are a lot of bands that have no keyboards but there's enough that do to make it worthwhile. ****, I want a Progressive Rock Band with keyboards and all sorts of pretenious 10 minute songs by Genesis, Yes, Pink Floyd, etc. And then for like Jethro Tull you blow into the mic for flute solos! This is only a sorta serious idea.