I was forwarded a link to an article on the Playstation Blog this morning that stated Sony has announced that all of the instruments in three upcoming music games (Rock Band 2, Guitar Hero: World Tour, and Rock Revolution) will be compatible with each other.
At the bottom a Gamasutra article about the blog post it stated:
"Similar music game peripheral enforcement has yet to be enacted (or at least officially announced) on the Xbox 360 platform."
For the record, we also do that, so consider this an official announcement.
All the instruments from Rock Band 2, Guitar Hero: World Tour, and Rock Revolution will be cross-compatible.
In other words, welcome to the party.