Is there a reason why Activision and Harmonix parted ways? It seems like Activision just stupidly created their own competition.
Rock Band is pretty much "Guitar Hero with more instruments". If Guitar Hero is retooled to include more instruments then what difference will there be between the two series?
Considering Rock Band is more expensive than Guitar Hero I would argue that there's a reason for the two to co-exist. If Guitar Hero becomes multiplayer focused and requires more insturments then where's the single guitar alternative for someone with a lower budget or who perhaps wants something more single-player focused?
I predict that Activision and EA will, as typical for them, milk the f*ck out of two series that are almost exactly the same and everyone will get sick of the whole concept. Then both companies will take a huge loss when the sales dry up and they have a huge unsold stock of the latest sequels and corresponding accessories. Hell even ignoring the existence of two virtually identical series, at what point does it no longer make sense to sell the game as a bundle with the hardware? Eventually you figure the amount of people who own the accessories and just want a copy of the game will exceed the amount of people buying it for the first time. Right now the selection I see in stores suggests that they're relying on people to not have the hardware yet (this is obvious with Rock Band since it's new).