Step files work well for interchange but have no parametric features as far as I can tell. They are also proprietary. For whatever reason, I haven’t seen any serious effort to make an open source cad kernel. Maybe one reason is unlike 3D modeling for artistic domains, very few users are capable of working on software and there’s probably much lower pressure to use software to automate design.

I don’t really see a need to focus on subtractive and additive manufacturing in the kernel, although some hints in the UI for a particular program would be useful. Analysis and optimization predates 3D cad, in a way so it would be interesting to see what could be done from scratch.