I don't know if every emulator that achieves 100% compatibility does so out of trying to do just that. It may be the case that a system is so basic and primitive that writing one to play them all is trivial, or as I pointed out with Mednafen's VB emulation, the number of games to perfect is just surprisingly low.
Higan truly is an amazing piece of software, but remember, after a certain point, there's no need to go any lower in low-level emulation. It may not emulate things on the transitor, molecular, or atomic level, but emulating each hardware component in software is just "enough". When you get down to it, all the program has to do is generate the correct pattern of lights on your screen and push the correct pattern of signal pulses to your speakers at the right time. There are a lot of steps to achieve this, but from the previous viewpoint, nothing says it can't be done in software. Just pointing that out since a lot of people always throw around the concern that emulation might need to go even lower level than we've seen it go so far
Higan truly is an amazing piece of software, but remember, after a certain point, there's no need to go any lower in low-level emulation. It may not emulate things on the transitor, molecular, or atomic level, but emulating each hardware component in software is just "enough". When you get down to it, all the program has to do is generate the correct pattern of lights on your screen and push the correct pattern of signal pulses to your speakers at the right time. There are a lot of steps to achieve this, but from the previous viewpoint, nothing says it can't be done in software. Just pointing that out since a lot of people always throw around the concern that emulation might need to go even lower level than we've seen it go so far