6) Quasar
You know Green Lantern, right? Well, Quasar is pretty much the Marvel universe’s version of the Emerald Knight. Quasar’s powers come from the Quantum Bands, a pair of wristbands which give the wearer extensive light based powers. Whoever wears them is designated the Protector of the Universe.
A bunch of different heroes have donned the Quantum Bands and become Quasar over the years, but the best choice for the films has to be Wendell Vaughn. As an everyman who’s thrown into the world of cosmic danger and adventure, Vaughn would be the perfect choice to lead the second iteration of the team in the wake of Star-Lord.
In the comics, Wendell Vaughn originally worked for S.H.I.E.L.D. but was deemed unfit for field duty. It would be a canny bit of world-building and foreshadowing if Vaughn could be dropped into, say, a Captain America movie before becoming Quasar in Guardians of the Galaxy.