The other day we were talking about I/O options (in the context of my apparently controversial BASIC computer) and while I was researching tact-switch based keyboards I came across this:
https://hackaday.io/project/158454-mini-piqwerty-usb-keyboard
This one is USB and designed to connect to a regular computer, but I think I could modify/extend it to work with my all-in-1 design.
I also came up with a somewhat novel output device but I’ll save that for another toot.