As I understand it, part of the reason Weller was cast in the first place was because he was physically slight enough to fit inside the costume and was a trained mime, so he had the physical discipline to move like a fluid machine. That's somehting the other Robocop actors never got quite right: the walk. Weller's walk isn't nearly as jerky and mechanical as the others and was in fact deceptively elegant. There's an economy of movement involved that is missing from the later performances.
So whomever they cast for the reboot, I imagine it will be another relative unknown with a background in dance, mime, gymnastics or something similar.
Of they could just hire Doug Jones.
Yeah it's amazing to me that the other actors couldn't even come CLOSE to moving like Weller did in the suit. Maybe some of that was just them wanting to bring their own style to it, but whatever the case, it never looked half as good.