This is a general curiosity and not a critique ... but why exactly are you listing SNES + SuperFX as a separate machine, in this case, "snesfx"?
for the exact same reason, we need a separate system for Genesis + SVP to play the only game released with this add-on chip (Virtua Racing)
at a point, I hope it will be possible to add CPU at start/reset: it would be extremely handy to add/remove floppy drives at runtime [1] to systems which now require a separate entry for the system + floppy configuration...
how far MAME/MESS is from such a point, only Aaron probably knows...
[1] or by performing a hard reset
