Eu acho que uma razão no universo não faria sentido, uma vez que a Marvel criou um novo universo para esses filmes - o universo cinematográfico da Marvel.
Dito isto, há planos para fazer filmes Hawkeye e Black Widow.
Black Widow Solo film in discussion
Marvel Studios head Kevin Feige has confirmed that discussions are already in the works to have Scarlett Johansson reprise her role as Natasha Romanoff in a Black Widow spinoff film, though the project will take a backburner while The Avengers is in development.
E:
Black Widow, S.H.I.E.L.D., Hawkeye, And Dr. Strange Movies Planned Post-'Avengers,' Says Kevin Feige
Black Widow, Hawkeye, and the spy organization, S.H.I.E.L.D. — all of whom are more than worthy and capable of carrying their own films.