Here’s a scoop from the Marvel big boss, although, beware apparent minor(ish) spoilers for Thor: The Dark World. There’s definitely a bit about Loki that I wish I had not heard, but overall I doubt if it’s a very big deal.
So apparently Thanos will be appearing in Guardians of the Galaxy as the mastermind. And as I’ve already mentioned briefly, Ultron will indeed first be seen in Avengers 2. I’m glad that Marvel seems to do a good job of knowing what things to keep in the cinematic universe, and what things are okay to tell differently than the comics.