This is similar to the level of "brain transplants" it seems most remaining classic-Amigas has these days (accelerator boards with FPGAs + a graphics core and what-not on the FPGA in addition to the CPU core + fast RAM), to the extent that the original boards are increasingly mostly a fat keyboard with IO ports.
On one hands these hacks are quite cool. On another hand many of them are pretty much full computers where going the whole hog and replacing the motherboard is increasingly looking like the better alternative..
E.g there's a "emulator in a C64 cartridge" that's powerful enough to emulate Amiga's, where the C64 is basically just turned into an IO device when it's plugged in - but at least there's some poetry in that, as some Amiga models - A500(+) and A2000 at least - had a 6502 compatible SoC as the keyboard controller.