The lack of Ant-Man had been announced by director Joss Whedon a few hours before the San Diego Comic-Con Panel that assembled
The Avengers cast on stage. And apparently Edgar Wright's script for
Ant-Man's solo film may explain why the mini Avenger won't make it
The Avengers debut, though he was key component to team in the comics. . Speaking with
Cinema Blend, Wright says....
"I talked to Kevin Feige about that a while back where we just discussed about whether he would be in The Avengers. The thingis, the script that I’ve written, you know, whether it’s next or not I don’t know, the chronology of it or the way it works wouldn’t really fit in with what they do. And my film is very much an introduction to that character, and so it wasn’t something where it felt right to introduce him in that film. Maybe if I do the solo Ant-Man film and maybe there’s a later Avengers then they could draft him in later. But it didn’t work with the kind of the angle that we were going to do with the origin that I’d written."
DCMF - The way I see it is, there is no way Marvel Studios will produce a solo film for Ant-Man, without him being apart of the
Cinematic Universe. So despite what Wright says, Marvel can easily weave the current Cinematic Universe with Ant-Man's even if the script doesn't say so. Only if it isn't too out of place of course. But if he really doesn't make in the Avengers live-action debut, you can guarantee he'll make it in the sequel.