As noted, Ta-Nehisi Coates is writing it. If you don't know him, Google him. He would not be brought in to write another white superman story. That doesn't mean we won't have a white superman too, because I'm kind of doubting Warner is going to put $200 million into an unproven commodity like this just for fun, and they already have a black Superman of Earth 23. No reason not to have a meeting of the two. The multiverse is pretty well ingrained in the DC TV shows, they just haven't toyed with it in the movies yet. With that said, it sure would be easier for him to write a John Stewart Green Lantern. Most kids out there identify Green Lantern as him nowadays. Mind you, the DC history of Black Kryptonians implies that there may have been some discrimination (and all black kryptonians come from one island on the planet (although it might be really big, i dunno), although I don't know if Earth-23 (and thus Krypton 23) had that history too. In Supergirl it seems implied that Kryptonian society had its share of classism and snobbery, at least that's what the Daxamites think, of course, they're jerks too.