Not to trivialize QEMU (I use it often and I love it) but usually the challenge with console emulators are A) emulating supporting hardware such as graphics chi

Not to trivialize QEMU (I use it often and I love it) but usually the challenge with console emulators are A) emulating supporting hardware such as graphics chips which are often undocumented and B) achieving cycle accurate emulation for platforms which need that. QEMU emulates relatively standard hardware for each platform. Even for x86, sometimes I find 86box or PCem more desirable for certain older hardware/software vs QEMU.