Great educational project and it does look neat: kind of tiny Altair.
From philosophical POV though I’m not sure that say running a modern 32 bit CPU to arbitrate a bus to Z80 is any more rational than doing all in 74 series :)
I’m not sure I get the point. If you want to write code for a tiny, resource-constrained CPU you’ve got the ESP8266 module sitting right there …
Apart from the “retro” factor, it is actually a very different experience developing for a Z80 compared to an ESP. You can really write code from scratch for a Z80, and also you will have to learn at least some basics about digital electronics like how to connect RAM, EEPROM, etc. For the ESP you surely will end up using a provided SDK and since it’s a SOC with everything integrated it “limits” what you can really do.
You can also troubleshoot and test by observing and manipulating the signals on the bus, which I think is the greatest reason to play with an old microprocessor vs a microcontroller or modern SoC.
FAP80: Retro-computer porn.