Nice idea! But it's far from original. It's already been done on A500, not as an accelerator, but as a hardware emulator;
http://www.amiga-hardware.com/showhardware.cgi?HARDID=333The idea was to load MS-DOS and Windows using the NEC version of an 8080 on board, thus effectively having a fully fledged PC inside the Amiga. A friend of mine at school had one and it worked beautifully. Of course, there was no GUI integration as you envisaged.
Still, with the low power cheap Geode and a custom northbridge I believe it's duable!
