Are there any KM or KVM switches which work via the keyboard?
I remember in the past there were switches which would use a particular signal from the keyboard to initial a switch, allowing you to switch right from the attached keyboard. All the ones I see now-a-days have either buttons or remotes.
ATEN seems to make some, like the ATEN CS62U, which I've thought about getting.
KVMSwtichesOnline (https://www.kvm-switches-online.com) has a search capability with a filter for "Switching Method" that includes "Hot-Key Combos."
Maybe not what you're after, but the Logitech MK850 wireless bundle has three buttons on the keyboard which allow you to swap between 3 computer pairings, which is pretty good. The mouse has the swap button on the bottom, which is kind of a bother if you're swapping a lot.
Every KM switch I've used switches via a mouse movement. It's not quite a keyboard, but at least it isn't a button or remote. :/