There's too much information here that my brain is melting with excitement. Which is odd, but totally awesome.
Firstly, the keyboard peripheral has finally been revealed! The peripheral is a full 25-key keyboard, with easier difficulties utilising the same five colour system that the other instruments have and the higher difficulties (and the new authentic Pro mode) using all of the keys, with the stream of notes shifting left and right to correspond to the correct keys. The keyboard has been confirmed as being able to be used as a full functional MIDI keyboard that you can hook up to a computer if you so wish.
So about that Pro mode, I'll quote you the brief description of the game from Harmonix CEO Alex Rigopulos which sums it up pretty well:
If you are a really casual player, you just like to play at parties or whatnot, we are offering a bunch of great new seamless party play. If you are looking for something new, of course we are adding the vocal harmonies and the keyboards, which lets up to seven people play together and is a helluva lot of fun in a social party context.
If you are someone who is looking for a deeper challenge either because you are an expert player looking for the next level of challenge or because you actually have musical aspirations, there is the Pro game play (mode), which is really going to start to close the gap between simulated music and real musicmaking.
But not only is there a new keyboard controller, there's also been confirmed that there will be two advanced guitar controllers that similarly take advantage of the new Pro mode, one of which is a full-size Fender, though details are still slim on that for now. But don't fear: all previous peripherals will work with the game!
As mentioned above, the game is also confirmed to have drop in/drop out gameplay so players can change instrument, difficulty or just stop playing at the drop of a hat without ending the song or inducing any sort of kerfuffle.
The song menu has also be revamped and improved, which is definitely a pretty essential update for RB3 if you ask me. With the amount of songs available now through the entire Rock Band Library (including the exports of previous games and track packs, all the DLC in the Music Store, the Rock Band Network and the 83 songs on the RB3 disc), finding the songs you want definitely needs improving over Rock Band 2's current system.
22 songs of the game's setlist have been confirmed too, which are:
• The Cure - "Just Like Heaven"
• Dio - "Rainbow in the Dark"
• The Door - "Break on Through (To The Other Side)"
• Huey Lewis and the News - "The Power of Love"
• Ida Maria - "Oh My God"
• Jane's Addiction - "Been Caught Stealing"
• Jimi Hendrix - "Crosstown Traffic"
• Joan Jett - "I Love Rock and Roll"
• Juanes - "Me Enamora"
• Metric - "Combat Baby"
• Night Ranger - "Sister Christian"
• Ozzy Osbourne - "Crazy Train"
• Phoenix - "Lasso"
• Queen - "Bohemian Rhapsody"
• Rilo Kiley - "Portions of Foxes"
• Smash Mouth - "Walkin' on the Sun"
• Spacehog - "In the Meantime"
• Stone Temple Pilots - "Plush"
• Them Crooked Vultures - "Dead End Friends"
• The Vines - "Get Free"
• The White Stripes - "The Hardest Button to Button"
• Whitesnake - "Here I Go Again"
For an amazing five-minute showing of the game, check the external link below for USA Today's video. The video shows a number of Harmonix employees both playing and talking about the game, including footage of the new keyboard peripheral and more. It's probably better to watch that than read any of my incoherent spiel.
Rock Band 3 is scheduled for release at the tail end of this year.