Just before E3, Harmonix let the cat out of the bag on Rock Band 3. Introducing not just a keyboard interface, but also a Pro mode, which allows for both midi input and instruments designed to replicate the real thing. Now you will be able to plug in a real midi drum kit, a 120 button guitar replica guitar, a real guitar with midi registers (made just for this game), and/or your own midi keyboard. Still waiting to hear if any guitar with a midi pickup will work. If so, I think they just out-hero-ed Guitar Hero by a mile.
Sound like too much? Well, as long as they keep the standard mode intact (they will), to me it only opens up a new avenue for not only actual musicians, but for music learning, as well. Video games have been the bastards of media for far too long, imo. The phrase "learning can be fun" has always been cliche to the point of being cringe-inducing, but really, if you are going to learn something why can't it be during a fun game?