Joss Whedon's at SXSW to do some press for Cabin In The Woods, the upcoming horror film that he wrote and produced alongside Drew Goddard. That film has been on the shelf for over two years now, but now that Chris Hemsworth is starring in Thor and another summer movie this year, it makes sense for it to finally see a release. So, of course, whenever he sits down with journalists, all they want to do is talk about The Avengers instead of the movies he's there to talk about. Surprisingly, in what was perhaps an unguarded moment, Whedon confirmed that the alien invaders in the film won't be either the Skrull or the Kree, the two races that had been considered the most likely candidates to invade Earth.
Those two aliens are Marvel mainstays and have enormous backstories. They have a big life of their own that just could not be contained in a film where I already had seven movie stars.
That's not necessarily a huge revelation, since Kevin Feige had, I believe, long-ago hinted that the Skrull weren't in the film, but it still leaves open the door for interpretation as to who, precisely, are going to be the bad guys in the Avengers movie. Since Loki re-appears, it'd make sense for the villains to be some kind of mythological race, one could suppose, but then his powers of manipulation are such that it could be basically anyone.
The Avengers doesn't really look like it's going to be focusing on the external threat, though; it would appear more likely that it'll be the team-building episode of what I'm sure Marvel wants to be a trilogy. Still, it'll be interesting to find out precisely what the Avengers are actually fighting in the film. We'll know in May, at the latest.