How feasible would it be to develop a CPU upgrade board around an RP2040 that would plug into the 8088 or 8086 socket (and perhaps also into the 8087 socket) of a PC/XT machine, and emulate a 386 class CPU, or perhaps even something faster? A drop-in replacement of our vintage computers that would provide them with a faster (emulated) x86 processor as well as more (and faster) RAM. Other than that, the host system would be used for any other I/O.

Basically, this would be a modern alternative to those quite rare 286 accelerator boards that were developed for 8088 an 8086 systems back in the day.

It might not even have to be a full add-in card with ribbon cables to the CPU (and FPU) socket(s). It could perhaps even be a pluggable module in the same vein as the Pentium Overdrive upgrades.

In the special cases of the PCjr and Tandy 1000, an additional challenge would be to clone the shared video memory regions to the actual RAM on the motherboard (just writing it out to keep the graphics controller in sync with the internal RAM of the CPU upgrade).

Actually developing something like this would be well beyond my technical expertise, but at least in theory, something like this seems feasible, right? 🤔