I agree for older machines this is a great approach. A lot of the challenge is being organized and persistent, powering through all the opcodes and making sure they're accurately implemented. I made a Sega Master System emulator many years ago and it was a fun project.
I do wonder how one takes on modern machines though. It seems like it'd be a completely different ball of wax.
Modern game consoles have a lot of common library / OS system calls that instead of emulating you re-create those calls and make your own implementation with the expected return values. The low level stuff and shader translation aspects are very complicated though.
Oh definitely, writing an emulator for a modern system is an entirely different ballgame. I truly respect the dedication and skill of the people behind large emulator projects like PCSX2 and Dolphin.
I do wonder how one takes on modern machines though. It seems like it'd be a completely different ball of wax.