Yeah, I've got to be honest here: I once tried to make some improvements to the MESS SNES driver's video hardware emulation. I ran, screaming, within 5 minutes, because it has practically no similarities to any other emulator's codebase.

I'm pretty sure that devices can have their own clocks now, so I dare say that the driver would seriously benefit from just scrapping the entire video hardware emulation and duping the g65816 core into an S-CPU core, and then trying to take as much of bsnes's code as possible.