I think we "know" Pym isn't in it cause they've been toiling on about his solo film for some 4yrs now. I think they actually want to do a fairly in depth look at an Ant-Man origin film.
While I'm for that and think Ant-Man is underapreciated they should find a way to have him at least cameo here and then flesh out his origin later in the solo film....if it ever gets going. He is a founding Avenger afterall.