Well being from the African American community myself, I'm highly skeptical they will represent a huge segment of the community overall.
African American's can hold two thoughts in their mind at once. They can be ,and are fond of, the white iterations of Superman, but they will also give a black Superman a chance , so that's not even an issue. Any fanboys hoping that Blacks will turn their back on a Black Superman is kidding themselves.
The bottom line is there are going to be people who can't accept the idea of a Black Superman, Clark or not. If they're that outraged about it, they won't see it, and WB certainly shouldn't be so naive to be surprised if that happens.
So yes, there's going to be a backlash , though the response to the idea of a Black Superman has actually been more divided in fandom then I thought, i.e. there are alot more people open to it than alot of fanboys would like.
The question is , how many people will see the film and give it a chance.