I think it should be contextual like in Dota 2 where if you're in mid lane and you use the missing chat wheel it'll say "Missing mid!"
In Deadlock it could say the hero name if it knows what hero is missing.
The 4 creeps per wave solution wasn't perfect but it was much better than this. Even worse is that you have to just remember which lanes were solo and which were duo; there is no visual indication.
If both are bound to the same key, pressing it causes you to jump off the zipline (because by default Jump and Cancel are the same key), so you no longer have access to the crouch-from-zipline behavior. Crouch should take priority because pressing Jump will let you do the default Cancel...
Can confirm that if you're using unit-specific hotkeys the Pause binding doesn't work. A workaround is to run this in the console:
bind P citadel_pause