are using extrudable conductive ink and claim to be able to make multilayer boards with their method. If one is going to go to 3D print may as well go one further and play with conductive ink. No, I don't have any connection to them. Just ran across the video the other day. https://www.youtube.com/watch?v=OqcAm7xGWJM
I do have reservation of thought on the use of conductive ink in high speed / high amp circuits but it may have limited application I guess in some circuit situations. Cheers !