There is software out there that will probe the surface of your uncut PCB (obviously with the aid of a suitable probe mounted on the Z axis) and then modify the G-code to make the tool follow the measured undulations. I think this is the sort of refinement that might be needed for SMD boards , though a machined flat base and double-sided tape is more my kind of technology.

I have enough unfinished projects at the moment so a new way of making one or two circuit boards per year is going to stay firmly OFF the ToDo list for now.

Kit