The decision to keep the Nolan trilogy of Batman films separate from the newly minted DC Film Universe was I'm sure not an easy sell. Batman Begins, The Dark Knight, and The Dark Knight Rises all made money hand over fist and had a hand in showing just how well superheroes could be translated to the big screen if done correctly.
That doesn't mean the studios didn't try and find ways to cross the films over, much to director Zack Synder's chagrin. Film Ink recently asked him about the possibility of Dark Knight actor Christian Bale reprising some sort of role in Batman V Superman: Dawn of Justice.
“This is a total and opposite reality from the Chris Nolan movies. It’s another universe, so we couldn’t hire Christian Bale if we wanted to, because he doesn’t exist in our world. Maybe we could hire him to play another part. We did talk about that briefly. I just wanted to hire Christian to play another part to make that obvious. Christian could play, like, Alfred with age makeup. No! Of course not. But you know what I mean. Even people at the studio would say, ‘Who are you getting from the other movies?’ And I was like, ‘Hey, come on guys, let’s all understand, it’s a different world.’ In the Batman universe that Chris Nolan created, Superman would have a hard time existing. That that’s why we did a reboot on the universe, so we could allow these characters to exist together. We needed to do that to have Batman exist in this world.”
While you might be able to stretch things here and there, ultimately I believe Synder is right about Superman having a hard time existing in Nolan's universe. The way Marvel winks at the audience, it is something they might be able to pull off, but having Bale in another role would just take audiences out of the film.
via Film Ink