Honestly, this is one of the most interesting ideas I've read in awhile. I know something similar was done with the Commodore 64 to emulate a hard drive. (64HDD)
I don't see how the hardware has to be overly complex if the expectations were set that it would emulate *existing* accelerator boards. (Or at least the speed expectations.)
I would think you would just find the simplest way to connect a cable to the expansion port of an Amiga 1200 (or Amiga 500) and connect it to the PC somehow. Via USB? Or parallel port? That'd be the first milestone. I'm betting the software part would be fairly easy for someone who could work with UAE's code.
Thanks,
Neofree