As expected, the guys at Neversoft are all about potentially using the DJ Hero controller in a future game. I guessed as much when DJ Hero was revealed to support the guitar controller for certain tracks. Guitar Hero director Brian Bright dropped the following quote on Eurogamer TV:
"We've worked with [DJ Hero creator FreeStyleGames], talked to them about the game for a couple of years now, looked at different builds and played it. We would love to integrate in the future."
Why isn't the functionality in Guitar Hero 5? Bright claims that "unfortunately for Guitar Hero 5, we ship a few months before they do... we'd love to explore instrument compatibility in the future; we'll see where it goes." That's certainly one possibility, but I'd put money on Activision and Neversoft waiting to see how DJ Hero sells before developing anything into Guitar Hero.
In any case, the DJ Hero peripheral would probably be pretty useful in the Music Studio mode in Guitar Hero. Just sayin'.