There's a line in the first Hobbit movie which seems like foreshadowing, when Gandalf asks Sauruman, Elrond, and Galadriel why it doesn't bother them that the last dwarf ring is unaccounted for.
If you combine that with Thorin's noticeable change in demeanor at times during the second movie (prompting Balin to say "You're not yourself!") - including turning his sword on Bilbo for a moment - I wonder if you have a plot twist where Thorin (the perpetually grumpy dwarf) is concealing the last dwarf ring made by Sauron.
Is this a plausible direction the last movie might take (perhaps from information from movie-related interviews or the like), or is there something that would make this unlikely that I'm overlooking in existing Middle-Earth lore?