Earlier quoted context omitted.
> It's actually a lot more work than you'd think to support this... Like: how would one support multiple keyboards? Is there an experimental or logical model for that?
Multiple keyboards is trivial - unless you meant multiple active cursors. (If you've used a USB keyboard attahced to your laptop - you've already experienced multiple keyboards. Both work.) Multiple mice is esoteric.
And at home, I have a mouse on the left side of the keyboard and another one on the right.