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@haitchfive I can, and I wasn't suggesting them as a replacement for Z80s (or any other eight-bit microprocessor).

Human-comprehensible silicon is exactly what Tiny Tapeout's about, though - to the point that it includes SiliWiz, an open-source browser-based tool to teach you how semiconductors work at the metal-and-silicon level:
https://app.siliwiz.com/

If you're interested and have a few minutes to spare, I've an interview about it all up on Make:
https://makezine.com/article/electronics/diy-silicon-design-your-own-chips/