@viv @djsundog get the https://www.analogue.co/pages/nt-mini people on the horn! they have a bunch of 8 bit consoles (nes, gb, sms...) implemented in fpga, which sounds like a reasonable starting point.

combine that with open source specs and firmware for controller adapters - http://www.raphnet.net/electronique/electronique_en.php#1 - and you've got yourself a feasible project... or so i imagine.