I like the idea of yokogawa's minimal fab, which removes the necessity of a clean room. It still needs plenty of fabrication steps, so you still need plenty of different machines and the entry ticket is ~10M.

I'm convinced that there are plenty of design space that is not explored. In particular, the fabrication process today is mainly 2 dimensional with a very high necessity of control.

If you relax one of this strong constraint and build the system bottom-up instead of top-down. It reduces to a search for the chemical compound, which can self-assemble into an interesting structure. It should look like a biological machine but running at computer frequency.

Plenty of nano-computing units interacting. For example today we can already build some silicon-nanorobots ( https://www.electronicdesign.com/industrial-automation/artic... ). Give each one a small memory unit, processor, and radio-link, and you can build tons of them on imperfect crystal using standard process. Then your processor is a 3d volume of these bots instead of a 2d-surface. You will still be constrained by heat dissipation but if you put them inside a liquid, it would be less problematic, but you'll have to compensate for nano-processor brownian drift.