'Chuck as the series Big Bad' definitely has me interested in the final season. I love when they mess with our expectations, and there are so many ways the show could take this plotline.
For instance:
Is Chuck just pretending to be a jerk?
Is there really only one Chuck in the multiverse?
Is Chuck's sister also a one-off in the multiverse? If so, how does that work with Lucifer's back story in the Michaelverse?
Is The Empty just for one universe's supernatural dead or all of them? Could Billy be working with her counterparts in other universes?
Could this all be a lead-up to the creation of our universe (meaning a place lacking in demons, monsters, etc.)?
We already saw our universe. Remember the episode were the brothers found themselves as the actors who play them and "Supernatural" was just a tv show.
Jason