Rock Band 3 is going to come with a real-deal MIDI keyboard. Yes, this new music game will attempt to teach you to actually play music.
Sure, it's a tiny little wiener of a keyboard, with only 25 keys, but it's a keyboard nonetheless. When you play in the new "Rock Band Pro" mode, you'll be using all 25 of those keys rather than just hitting keys in a designated area.
To compliment this new, more-realistic instrument, two new guitars are also in development that'll be closer to the real thing. Yes, that means they'll have actual strings, with one of them being a full-sized replica of a Fender Stratocaster and the other a Fender Mustang Pro.