In this one, Dave Darko attempts to create a wi-fi adapter for the original Gameboy.
https://hackaday.io/project/20769-wifi- ... -cartridge
IIRC, he originally started out with the idea of using a modern micro-controller (ESP32) to emulate a ROM chip.
You might think it would be easy for a micro-controller with a clock speed of 160MHz or more to emulate any given 80's era logic chip running at 4MHz/150ns clock. This would be particularly handy for replicating the various mapping and lock out chips that were used in carts of that era.
Sadly, in practice those chips are still not fast enough. From what I've read, while the controllers' CPU's may have the horsepower, the sticking point is their I/O ports are just not able to read the inputs and then switch their output state fast enough.
Enjoy.
Nick