She-Hulk
Bruce Banner’s cousin, Jennifer Walters AKA She-Hulk has to be one of the biggest Marvel heroes yet to appear in live-action in any form. Save a promo image for an 1990s movie that never happened starring Brigitte Nielsen. It’s bizarre, too, considering the cultural impact the Hulk has made, and something really needs to be done about that soon.
An all-female Marvel movie would be the best place to introduce She-Hulk into the MCU, then. For one thing, Jennifer is the leader of A-Force in the comics, so she would be a natural to take charge of the team on the big screen as well. She’s one of the strongest women – in terms of muscle and characterization – and could easily command the respect of the likes of Black Widow.
Also, featuring She-Hulk in a film that isn’t solely about her could be the only way she could make it onto screens. It’s known that Marvel can’t produce a Hulk solo movie due to ongoing contractual issues, but he can take part in team-up films (e.g. Avengers, Thor: Ragnarok). It’s likely that something similar exists with his female counterpart, then, but an A-Force movie could easily scout around the issue.