as far as i know there is only an alpha release of a snes9x-port with less functions, which is really slow. in fact a software implementation of processor-functions is slower as on the real hardware. i think only an experianced n64 developer could make a good statement, if it's really impossible or not. it's easier to make one for the newer console generations, so the benefit seems not to be very big in order to spend much energy in it cheers saturnu
It's possible to make a full-speed SNES emulator, but it will require a lot of speed hacks similar to late-90s PC emulators.