It just wouldnt make sense for a RB2 export right now. Since not all the songs will transfer over. You would be paying extra money for content that cant be used with any current game.
And the only way around that is for an RB2 export key that only exports the songs approiate for LRB. Then when RB3 comes out there would be ANOTHER for to export ALL of the songs for RB3.
In other words: it would be a cluster-f