[rm445]

Given that multi-layer PCBs are effectively laminations of individual boards, hobbyists have already made their own multilayer boards [1]. I don't see anything particular about milling as a means of copper removal that would stop you layering up boards?

[1] https://www.instructables.com/id/Flexible-Double-Layer-OR-Mu...

[archi42]

Thanks for the link, nice to know it can be done at the hobyyist-level. But it's still a lot of work I (personally) do not enjoy spending time with. If I had the space I'd probably setup my (hypothetical) MPCNC for milling PCBs, so I can do quick single layer prototypes (maybe some simple stacking using header rows), but anything more complex would still go to a fab.