I don't see any functionality that Doom Slayer could offer that Ash wouldn't. Chainsaw and shotgun? Ash could also bring in The Necronomicon, Deadites, his transformation, and Bruce himself.
Also on the subject of Robocop I'm thinking about it and I think they could make the same character but with more functionality if it was Judge Dredd. I'm really hoping they give Robocop some kind of armor mechanic, or like a tracking projectile or something. Robocop shooting under his arm without looking while getting shot from all sides is who he is and they need some kind of representation of that
I remember suggesting some kind of stance for Term where he walks forward and is immune to projectiles so something like that, but he really needs to be slow and plodding overall. We honestly need a character like that considering Kotal, Shao, Term, and Spawn all wavedash like they got propellers in their ass.
Chances are though his base kit will get a projectile, a combo ender, and some kind of neutral control tool. Then his variations will be a mixup one, a zoning one, and one with a launcher and some kind of match control tool