I'm inclined to agree with Droosies that the songs *will* be exportable to the RB series:
"This is not just a Rock Band expansion pack, it is much much more than that."
Key word, "just." If they'd wanted to say it's a completely separate standalone, they would've said "This is not a Rock Band expansion pack." The fact they included "just" indicates that it *is* a Rock Band expansion pack, with lots more added features.