I don't think MBJ's pitch included playing Clark Kent. It would've been Calvin Ellis, I'm guessing.
I agree with not preferring a racebent Supes, but for selfish reasons - unlike some here, I still haven't seen MY Superman in a movie. I didn't like the Reeves version, didn't like the Snyder version. If I had loved one of those, I'd probably be fine with them changing it up, but I still haven't seen the Superman in my head that I read in comics and grew up watching in animation all the time brought to life in a film, so until they nail that version in my eyes, I'd prefer they not move onto something else. I think there's still a great modern Supes film featuring the traditional Supes that hasn't been made yet, and I'm dying to see it.