This would absolutely have to be exportable. I'm fine with a limited number of full band games if they're done right, but what I hate about Activision's model is that you can lose track of what disc you need for what song, especially with their ridiculous decision to include "similar" artists. Because, you know, when I think about Metallica, I think about Lynyrd Skynrd (sic).
I'm fine with knowing "okay, if I want to play Beatles songs, I put in TBRB, and every other group is the main RB game." What I would hate is thinking "wait, was that song on the first TBRB or the second?"