I agree with alexh. There is no way this can work without huge compromises...
- Synchronization would be nearly impossible. You can't stop or slow down custom chips without side-effects (or lost data)
- How to get sound and video back to host? What about all kinds of random i/o-signals needed? It won't be trivial.
- There is no need for fast CPU and custom chip emulation. Emulated gfx card modes don't use or need custom chips and most games that need custom chip modes won't work with "too fast" cpu or bus..
Things that are easy in software can be extremely difficult in hardware and vice versa..