Probably the way to go would be add CyberGFX or P96 support and treat it like an RTG card.
Isn't the Indivision doing exactly that? It's a FPGA chip programmed to emulate the one on the motherboard, and also adding some nice things like RTG for Workbench. Along with a Vampire you'd actually be running two FPGA systems and emulating both the CPU and the Graphics system. Correct me if I am mistaken...
