It seems that QMK even has some basic support for the PS/2 interface. Not that it would come up very often, but a “retro” mode might be an interesting addition to your next custom keyboard build.

My version of remaking Rob Cai's Arduino Basic PC With VGA Output, which is to use two Arduino AVR boards to create a 8-bit home computer running the TinyBasic runtime with VGA video output and PS/2 ...

This Arduino BASIC interpreter will make a really fun one-day project if you’ve already got the parts on hand. [Usmar A. Padow] put together an Arduino Uno, SD card, four line character LCD, … ...