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