I wonder if one day, 3d printing will be cheap enough so that one could go to the local hackerspace, Print print out chips, assemble the board/internal devices and be sure to be free from hardware backdoors?

This is feasible today. Although it takes a decent skill set. Open source communities like OpenCore.org have enough FPGA architecture to build your own RISC computer from scratch. I suspect as FPGA's become more popular and speeds improve the hacker community will move towards one-off computers they made themselves.

This coupled with your idea of 3d printing for casing is interesting.

Doesn't that just offload the backdoor potential to the FPGA rather than a CPU?

I think it would be impossible, from a computer science standpoint, to create a backdoor in an FPGA that could compromise your own OS, in a general case. Perhaps, the computer that you use to program the chip could be compromised, to change the code that is put on the FPGA.

When I wrote that, I was under the assumption that people would use open-source CPU designs from OpenCore for convenience. With a little help from Xilinx and Altera, it wouldn't be too hard for a government to have the synthesizer detect when an OpenCore design is being used and surreptitiously put a backdoor in. I admit that it would be hard to write software to simultaneously detect a completely unique CPU design is being synthesized, figure out its instruction set and weaknesses, and finally create a hardware backdoor that could circumvent any software written for that device.

As always, there's a tradeoff between cost and security. How many hardware hackers are good enough (or motivated enough) to design their own brand new ISA and CPU design, then bootstrap a compiler and OS for their homemade CPU? Maybe 0.001% of the population, if that.

Well, I'd be down to try at somepoint, if I knew where to start. I feel like moving forward from now, in general, the future will require these skills in order to maintain some sovernty over onself.

I was wondering about that too. So we're down to buying silicon wafers in the the mail, 3d printer or some set up to dope them using open source designs? Is this possible now?