I would argue that Bale would fit perfectly in the universe created in Man of Steel. In Man of Steel the world before Superman arises is very much the realistic world in which the Dark Knight movies were established. If you think you need a campier Batman, I'm not sure how THAT would fit in with the Man of Steel.
I think trying to replace Bale gives you a great chance at failing with a new batman than succeeding. If I'm Warner Bros, I'm going to go to every effort to convince Bale to be in more movies.
As for Batman going up against Superman, I think the idea is ridiculous. And would at least hope that, that isn't the focus of the movie for very long.
I don't think you can make the case that the Hulk and Captain America are in the same league, yet they were able to pull it off. Batman certainly has a role to play, but it has to be done appropriately.