Originally Posted by Eddie
This. There's an interview with Kevin Feige for the first movie where he mentioned something along the lines of Loki being the only villain they referred to promoting the movie because he was more important than the aliens. That being said, at this point Thanos or Korvac seem just as likely.
That's because the Chitauri were nameless aliens without any lines. Just "Cannon Fodder #2" and "Dead Alien #3." The Masters of Evil would obviously be "name" characters with dialogue and personalities and backstories and everything.
Ergo: Joss Whedon was definitely talking about a singular villain for TA2. Not a group. Not the MoE.