Many many actors would love the opportunity to play Iago. It's a great role. There is no one actor who stands above the rest.
It is unfortunate, but black actors would probably not be allowed to play the part because of their race. This is because Othello is thought of as "a part for a black actor" and many people would be outraged at the idea of a white man playing the part with dark makeup. Consequently, the parts of Iago and Desdemona are not going to go to black people, but to white ones.
If Othello's blackness was thought of as a makeup issue rather than a racial restriction on the casting of the actor, then Iago's and Desdemona's whiteness could also be makeup issues and black actors and actresses would have a chance at those roles.