Analyst Group Janco has announced it expects Activision to expand the Guitar Hero franchise from just a Guitar and add its own instruments similar to what EA and Harmonixs Rock Band is doing now. Janco says they expect this will be a part of the natural product evolution as Rock Band provides a compelling option for the music oriented category. Also it wont be too bad for Activisions bottom line as the game is developed in-house with Activisions own developers. EA is only distributing the game and therefore receives less profits.
Source: Gamasutra