Buttons: by looking at the electric schema it seems possible. There are multiple controller lines left unused, so the buttons can be added and the firmware can be modified to read them. Is it worth it? Probably not.
Metal bearings: thanks, I will try lubricating them.
Dactyl-Manuform: I love that design, that's the best keyboard design (well, before this fish ladder thing, but amongst all other non-flat designs DM is the best option.)
I've been using them for a few years, this is the latest version that I've been using the last year and a half:
https://www.thingiverse.com/thing:4220567I don't see a need in anything bigger, 4x6 covers all my needs, typing, cursor and mouse control.