There is a formula to Batman that I dont see WB straying away from quite a while. Crime, terrorism,psychological film etc. At best I can see them branching in to horror with a psychological edge. Guys like Clayface and Man-Bat will be offered by many other franchises both with in DCEU and outside of it. I can see them as opening fodder but as lead villains? nah.
Again Prometheus gimmick is that he has plans to take down people like JL. He is toothless in a Batman film? I actually like the character btw.
Anti-Batman refers to characters who dedicate their minds and bodies for the pursuit of one single-minded goal. These characters are Batman's equals conceptually, they just exist on the other side.
Black Mask is not that guy, he's a weak willed thug who's not particularly good at anything except maybe torture.