ATTiny-B-W-VGA VS vga-rpi

I followed Ben's guide to make a little ATTiny 2 colour VGA output of a clock counting down. https://github.com/duncanspumpkin/ATTiny-B-W-VGA

It was quite a challenge building it into such a tiny controller. Was doing it for a University project where we wanted to have the clock started from an external source so needed to keep one I/O free for that input. It ended up with every I/O pin of the 8 pin micro having a use.

I've been sort of pondering the thought of using a microcontroller as the base of an ISA "soft video" card for vintage PCs.

I was looking at things like the Graphics Gremlin and the kit to build a Trident 9000-based ISA VGA card, and realizing that 1) I don't think my skills or gear are up to SMD soldering, 2) at least the Trident part is 20-year-old stock with limited supply and questionable reliability, and 3) you still end up with an analogue output that needs a chain of adapters to drive a DisplayPort or HDMI monitor. I may as well just use my old Realtek RTG3106 card.

I'm picturing a board that did some minimal decode of the ISA bus to filter accesses to upper memory or desired registers, then plumb the rest of the bus onto the RasPi GPIOs, and just run some emulation code to interpret the requests and maintain a framebuffer-- drawn to a HDMI output.

I figure by doing the emulation in software, you could cover a wide variety of cards and trivially switch (i. e. toggle between Tandy 1000/PCjr style CGA+, Hercules, and VGA, with some software command rather than having to physically change cards or detach the monitor).

It feels like something like this would exist already, but the closest I've seen (https://github.com/eyalabraham/vga-rpi) is not a drop-in replacement for a standard PC card-- it seems to expect custom hardware and BIOS shimming.