This is pretty much about writing a cpu emulator. A system emulator is much more complex even as far back as a gameboy or Sega genesis. I think there is still great value in writing your own cpu emulator as described in the article.
I used this website for information for both a Chip8 emulator and later an NES emulator (which uses a 6502). The PPU for the NES was definitely more of a struggle but Emulator101 is still a great resource even if you want to go on for emulating other chips / peripherals :)
