Indications that some sort of key-based instrument would join the existing stable of Rock Band peripherals--guitars, microphones and drum kits--arrived earlier this week, as a teaser image for Rock Band 3 prominently displayed the iconic black and white keys of such instruments. Ars claims that "the keytar will be the only new instrument for the game" and will be made by Mad Catz, which has been named the "principal Rock Band videogame peripherals partner."
In addition, Ars reports that "there will be a 'pro' mode included in the game that will require proper technique," noting that "all this information is firmly in the rumor pile, excluding the Mad Catz connection, but ...we're confident in this data."
More information is expected during E3 2010, which runs June 15 through June 17. As for Rock Band 3 itself, it's due on PlayStation 3, Xbox 360 and Wii "this holiday season."