I agree, multi-layer gluing and pre-made ground planes would probably work. The big issue is how to connect the layers, I don't see how to do vias either.

Maybe there will be a symbiosis of this and 3d printer, where the single pcb layers will be printed, using conductive material and non-conductive filler.

But however this is going to turn out, we are witnessing the birth of home electronics manufacturing. This will be significant, at least as much as the availability of high-quality consumer paper printers in the 80s/90s.