Caustic

This movie is an adaptation from Frank Miller's graphic novel, the Dark Knight Returns. This comic novel is near legendary now, and well written, mostly because it makes it plausible for Batman to beat Superman. If you don't know about the book and like the genre, I recommend getting your hands on it.

It also was a pretty fun read because it heads into the near future, where Batman is aging and retired, and Superman has moved into a darker place, motivated by his self righteousness and the ends justifying the means. It really exposes the character flaws for each superhero, which is sorely needed. As someone mentioned before, they always win.

I don't know if it would be a direct adaptation, I hope it is. It would be a huge win for DC to do something different from Marvel.