Remember in Eldest, when she had an argument with the dwarf priest? She seemed very Aloof. I mean, Elves are usually near atheists, but she was pushing it. She only realized he behavior in Brisingr- Inheritance and changed. "I'm not one of your helpless women, Eragon!"
I know this is theorizing. It points out evidence to believe that Angela and Tenga are descendents of the grey folk. Maybe those two are also descendents of the Grey Folk? But that is just what I think.
I think they will add a new storyline, and I do like the prospect of new, Dark Magic riders. Chris should also try to tie up loose ends in the series. A spin-off about Brom (made by Chris) explaining the old dragon riders would be quite enjoyable. Anything is possible.