I'm really projecting that it's going to be more of a game-changing mass expansion than anything. Retool the progression system to be different than the current light level system and convert everything over to the new way of doing things. Those that upgrade get to keep everything, those that don't stay on either the old systems or a limited version of the new one. someone else suggested it would be a lot like TTK; I think this is spot on, and TTK might have served as a proof of concept for that.