It's been one of the most persistent rumors of the last few months, with new life breathed into it by the folks over at GameNGuide who have been trying to connect comic book and movie dots to prove their case: Will Hank Pym, a founding Avenger in the comic book source material, finally make his first big-screen appearance alongside Tony Stark in Iron Man 3?
It doesn't seem so farfetched--according to various sources, and seemingly confirmed by promotional images and the like, Iron Man 3 will be a loose adaptation of the Extremis storyline from the comics. That means that by the time Tony starts having problems with his fancy new armor, it's likely that Guy Pearce will be done with his "cameo" and he'll have to look elsewhere for technical assistance.
Not wanting to turn to S.H.I.E.L.D. (because after all, Marvel executives have talked about not wanting to have "Call the Avengers!" be the end-all, be-all answer for every problem in the solo films), perhaps Tony can recruit one of the greatest minds in the scientific community.
And then, when he finds out that FOX owns the film rights to Reed Richards, he can turn to Pym.
Chen Lu, the Radioactive Man, has reportedly already been cast for the film. As one of the Masters of Evil (he's been a member of more than one iteration of the team), Radioactive Man has a history with Pym, as well--and while one would assume probably no more of one than he has with any other Avenger, or than any foe might have with any single hero, a quick breeze through his Wikipedia entry would discount that, with at least a couple of times singled out where he's been defeated by Pym specifically.
According to GameNGuide, Lu was originally reported to be a recurring character in a number of Marvel movies back when Andy Lau was rumored for the part. Described as a good guy in Iron Man 3, the idea was likely that he would gradually turn bad, finally appearing in an Avengers sequel, or something like that.
None of this, of course, means anything concrete for Ant-Man. Still, he's a scientific hero, not a magical or fantastical one, meaning that the Guardians of the Galaxy or Dr. Strange teases would be more at home on the tail end of Thor: The Dark World, with the Avengers 2 teaser likely coming to Captain America: The Winter Soldier. The idea that Ant-Man needs to find a niche sooner than later or risk becoming one of those Hollywood properties that's always discussed and never really made (Wonder Woman, The Flash...we're looking at you!) suggests that getting the character into the film would be a great way to incorporate him into the larger Marvel Cinematic Universe and make his movie feel more "real." It could also set up a great tease later in the film where, if Pym were to help out Iron Man using his scientific expertise, he could have a coda near the end of the movie where you saw him working on his costume for the first time or something like that.