According to a snippet on G4, Neversoft's Brian Bright has said a new peripheral for Guitar Hero World Tour will be coming that is specifically for use in the game's music studio mode. Presumably it'll be something you can pick up only if you're inclined to dabble in GHTunes, which from what I've witnessed, is a hella scary program on par with most high-end music software. Speculation has it as a keyboard, but nothing solid has been announced.

Personally I'd love to see some mixing desks or something, Hip Hop Hero would be cool with wireless turntables :P

Yeah I can see it being a mixer of some sort.

Cowbell.