So far, this is just a rumor (and wishful thinking) so don’t get too excited … take this with a grain of salt until we get the official word from Marvel Studios:
Now that The Avengers is out, Marvel Studios head Kevin Feige is talking about different aspects of the film and the future of franchise. He noted that Tony Stark had an interesting relationship with the other characters in “The Avengers,” but for Iron Man 3, he will be separated from the Marvel universe.
“He can’t call Thor, he can’t call Cap, he can’t call Nick Fury, and he can’t look for the Helicarrier in the sky,” Feige said. Those comments are backed by the fact that Black Widow was taken out of “Iron Man 3” after the studio confirmed that Scarlett Johansson will be reprising her role.
This leaves many to believe that despite everything Feige has stated that there’s a good chance that Bruce Banner/Hulk (Mark Ruffalo) will make an appearance. Stark and Banner got to know each other quite well in “The Avengers,” and since Ruffalo has a contract to appear in six Marvel films, “Iron Man 3” may be a good place to show more of the character.
Meanwhile, Jessica Chastain (The Help, Take Shelter) has revealed that she will not be starring in “Iron Man 3,” stating: “Sorry to say that ‘Iron Man’ 3 isn’t going to work out. My schedule is jammed packed and I can’t fit anything else in. The press announced my possible attachment far too soon.”
We are keeping our fingers crossed! (Source)