According to Zack Snyder, certain individuals at Warner Bros. were having a hard time grasping the fact that Christian Bale would not be reprising his role as Bruce Wayne/Batman. So to hammer home that notion, Snyder wanted to bring Bale into the DCEU but not as The Dark Knight. Speaking to FilmInk, Snyder stated---
"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.”
It's interesting that Snyder actually went so far as to consider Bale play another character in the DCEU. What part do you think he considered Bale for - we know Jesse Eisenberg wasn't always up for Lex Luthor. It would also be interesting to learn who Snyder had those "brief talks" with - was it Bale? Christoper Nolan? Hopefully Snyder will shed more light on this development during the Batman v Superman: Dawn of Justice press tour.
Fearing the actions of a god-like Super Hero left unchecked, Gotham City's own formidable, forceful vigilante takes on Metropolis's most revered, modern-day savior, while the world wrestles with what sort of hero it really needs. And with Batman and Superman at war with one another, a new threat quickly arises, putting mankind in greater danger than it's ever known before.