Well, Thráin is listed on the IMDB page for the next film, so I'm really, really hoping we get something of his story. The thing is, since Gandalf hasn't been to Dol Goldur yet, I have a theory that Thrain is still there right now and Gandalf got the map and key somehow before he wound up in the clutches of Sauron. So it might not necessarily be a flashback.

Yeah. The waterworks will be out in full if they do include it, I think. And I'll probably just have a cardiac arrest in the theatre during the third film.