5) Major Victory
The Guardians of the Galaxy movies are mostly drawn from the modern incarnation of the team, but there are some nods to the original, very different iteration that debuted in 1969. Most significantly, Michael Rooker’s character Yondu was one of the members of the original Guardians. So far, he’s the only one to make it into the movies, though, so why not introduce another in an upcoming sequel?
Major Victory AKA Vance Astro has a complex backstory, but simply put, he’s a human astronaut with the power of psychokinesis who’s flung into the 30th century. In modern comics, the Guardians find him back in the 21st century, cryogenically frozen and possessing Captain America’s shield.
The MCU hasn’t properly dived into time travel yet, but the comic book excesses of the Guardians of the Galaxy would be the perfect place to do it. Even better, it would bring in a character who’s got a rich history with the team at the same time.