It appears likely that Harmonix is adding keyboard support into the next iteration of Rock Band proper. This morning, downloaders of the Green Day: Rock Band demo--which is available over Xbox LIVE for the Gold crowd--received something of a tease after finishing the bite-sized, two-song offering. After hitting "exit," they were greeted with a big old Rock Band 3 banner that displays pictures of two guitars, a set of drums, microphones … and a keyboard right next to the "3" logo.
I can barely play the drums in Rock Band when I'm sober, so I can't even imagine rocking out well with a keyboard. It's like asking me to go to the moon with a bottle rocket or something. But I'm sure someone here has mad keyboard skills and just a tad bit more room in their closet, right?