The upcoming sequel will reportedly delve into Hank Pym’s (Michael Douglas) early days with his wife Janet Van Dyne, and as such Peggy could factor into that narrative as one of Hank’s colleagues at S.H.I.E.L.D., along with Howard Stark (Dominic Cooper) and maybe even Samuel L. Jackson’s Nick Fury.
One could make the legitimate argument that Hayley Atwell’s Peggy Carter doesn’t necessarily belong on this list as she has already featured heavily in the Marvel films.
Having said that, she attained the bulk of her popularity during her run on her awesome solo series, Agent Carter, so she still fits the bill.
Moving forward, Peggy cannot appear in any more contemporary Marvel movies (for obvious reasons) but she could easily show up in a flashback sequence, and there’s no better opportunity for that than Ant-Man and the Wasp.