I think the idea is that if a second "keyboard" is plugged in while the machine is locked/asleep, it shouldn't work. Even for the scenario where you dump $BEVERAGE into your keyboard, forcing a hard reboot to be able to plug in another keyboard (and log back in) doesn't seem unreasonable.
Yes, suppose you have a mac mini and you plug in USB keyboard, oops it's sandboxed and does not work.