Been following this thread for a while, thought I'd throw my 2 cents in regards to the villain...
What if it is a partially rebuilt Vader? Or what if he somehow survived the fire in RoftJ and what we're seeing in the concept artwork is his robotic skeleton? kinda like a Terminator
I think most people assume that Vader is dead and gone for good BUT I wouldn't be at all surprised if they tried to find a way to bring him back. He is after all one of the most famous movie villains ever and a lot (not all) of fans would rather see a movie with him in it over a new villain. I don't think it's to inconceivable to think that they will resurrect him somehow.