This would not have been unchartered waters, as Usher has played Marvin Gaye before, during a guest-appearance on the TV show American Dreams. (Did anyone watch that show? It faded away pretty quickly).
Anyway, Usher has made it known that he would like to be the one to tell the story of Marvin Gaye, "Because I understand the conflict he had as a man."
Unless someone else comes up with a new script, there is a film Marvin Gaye inspired movie currently in production entitled "What's Going On," starring Jesse L. Martin - formerly of Law & Order .