Deathstroke is very much a nice foil to Batman, but I would like something along the lines of Black Mask too. Or perhaps Hugo Strange. I'd like to see Batman actually have to do some detective work in a movie. For example, I always thought Seven could have been a great Batman movie. If Deathstroke appears, I would hope that there is some mystery involved with another villain working behind the scenes. Deathstroke is an assassin FOR HIRE after all.