A teaser image for
Rock Band 3 on the end of the
Green Day Rock Band demo included a keyboard icon along with the established guitar, bass, drums and mic.
Ars Technica's reliable mole has a few tentative revelations--it's actually a keytar! Supposedly it's the only brand new instrument being released with the game, but
as we know Madcatz will be handling all the peripheral production and distribution, while EA and Harmonix will cover the software publishing. Madcatz will be releasing a number of different bundles, and considering the rumored "pro" mode, some of them might be the more realistic instruments that Dhani Harrison hinted at months ago.
Of course most of this is rumors at this point, but it's worth mentioning that Ars' inside source has been very accurate in the past.