Coming from a Venturebeat interview with Harmonix CEO Alex Rigopulos...

"I'll also say that we don't view Rock Band as something that's being left behind. It's something we’ll return to at the right point in time and reimagine it as appropriate for its time."

I don't know when that point in time is going to be, but I believe it's many, many years off. Gamers aren't anywhere near ready to see more Rock Band.