If we cross this with the Nolanverse ever, we need a young Superman seeing how they are retelling it anyways. Might I suggest (and I know I'll get flammed for it) Tom Welling? Here me out, they want Dark, Smallville has been getting dark and it can slowly build up to it in the last 20 episodes. You could then have the story be that he just became Superman and that Lex is missing and there's another Super-Villain around and go around that. The whole time, Clark Kent has to be his bumbling-bafoon self again (which Tom is really good at) to hide his persona. Have one of his enemies find out who he is. We've never had that in a Superman movie. I think if they WANT a dark film, they won't be able to just have it be dark just like that. We have Smallville, use it to your advantage as a slow transition.