One thing I always wonder about low-resource-usage emulation projects for old consoles with fixed game libraries (e.g. GBA emulating GBC), is why you can't just throw some heavy ahead-of-time analysis at the problem of statically recompiling the whole game library for the native destination architecture. Why write an "emulator" at all, when you know exactly what code you want to run, and know exactly what code that code should translate into when run on the target CPU?

I guess a potential problem would be that this requires shipping a (IP-infringing) copy of the recompiled game library with the emulator. But it doesn't quite: instead of a library of ROMs, you could just ship a library of hint files to turn the static-analysis step of the recompilation into a few seconds of work, such that you still need an input ROM and the dest-ISA program is only generated in memory.