I'm interested in the market for newly made motherboards, expansion cards, etc., where we've seen projects like the NuXT, Graphics Gremlin, PicoGUS, PicoMem, Snark Barker, etc, even projects to solve problems that didn't exist back in the day, such as the CRT Terminator.

The Raspberry Pi Pico and Pico 2 microcontrollers in particular seem to be showing their usefulness for these purposes. Where the dozens of discrete chips required to create a modern, say, EGA or VGA card, aren't being made any more, can you achieve the same thing by making the Pico use all of its resources to behave like said card?

I've seen a few proof of concept tier projects that use the Pico or Pico 2 as a "GPU" of sorts. You can do VGA or HDMI output with it and hold a framebuffer in RAM.

There are Pi Pico ISA card projects now that are doing some pretty useful things.

The Pico 2 has 520KB of RAM and dual 150 MHz CPUs that can be overclocked pretty significantly. Seems like enough to hold 256K of memory for VGA support, plus the code that handles commands sent from the bus, scaling nicely to higher HDMI resolutions so you actually get a feature improvement over using a real retro card, etc.

Here's another idea: how about creating a "chipset" with various microcontrollers filling in the gaps of chips that are no longer made? All the newly made retro motherboards are using NOS components. That's fine for now, but those stocks will eventually dry up, plus these microcontrollers can be had for comparative pennies.