They could have made bank with a Pepper Pots/R.E.S.C.U.E disaster movie. Some villain causes a natural disaster, Pepper suits up as Rescue to save people. Writes itself.
Or a Black Widow/Hawkeye team up, "What Happend in Budapest" or whatever. Generic-ish spy film with superhero action, stealing secrets from hydra or aim.
Or a Squirrelgirl audience POV Great Lakes Avengers after the success of Deadpool.
Or even a Beetle movie, about Beetle II as an anti-villain/anti-hero merc, could also work after an R rated Deadpool.
Or a screaming mimi/songbird audience POV masters of evil to thunderbolts movie, then letting them develop her as her own character for phase whatever.
Or a Monica Rambeu Photon/Pulsar movie, thats goddamn obvious.
Or a Runaways teen-team movie, replace spider-man with iron man and its super easy to adapt as a film even before they got the six movies worth of spider-rights. Normal teens find parents are evil supervillains, steal power, run, one turns traitor, parents find them yadda yadda.
Or an Elsa Bloodstone monster hunting movie (that could lead into Nextwave).
Or a Mantis/Moondragon followup to Guardians of the Galaxy.
Or a Darkstar led European team.
Or a Domino movie with Domino as a runaway government superhuman weapons project, with the Armageddon Project as a non mutant based superhuman research team.
Or a Firebird movie to expand on the mystical side of things, "finds a magic thing in a meteor in the desert" is probably the easiest possible origin story for a movie.
Or a Wildstreak movie, thats easy too, olympian is confined to a wheelchair but a family member gets them to aid in developing exoskelletons to help the paralyzed walk, become superhero.
Or a Meggan solo british movie where seing the avengers on tv is her catalyst to escape from the room her parents locked her in.
Or throw everyone for a loop and do a Wasp movie instead of an Ant-Man movie, just the same movie except with a female lead.