Literally just that RetroArch doesn't support any Nintendo system from the last 20 years?
https://en.wikipedia.org/wiki/An_Open_Letter_to_Hobbyists
whoops wrong link but fuck it, serendipity
https://en.wikipedia.org/wiki/An_Open_Letter_to_Hobbyists
whoops wrong link but fuck it, serendipity
Maybe retroarch itself doesn't emulate anything, but just provide a render surface/input abstraction to 'cores'?