Re: Who should play Thanos?
They will continue to tease Thanos in the Avengers until he shows up. You don't hint at the character in the first film, and ignore him in the second.
Consider the Collector is out there, there are more then a few ways to hint and show him for a little bit in Avengers 2.
"It's true. All of it. The Dark Side. The Jedi. They're real."