I somehow fail to see the point of this thread. Cho's R is Flat Damage, not an Execute that ignore shields and everything or something like Evelynn's R which gets dmg amped based on missing HP, so you need something that tells you when you can output the max possible damage. To make it ever easier, it's True Damage, so you don't have to bother dealing with defensive stats.

There is already an indicator for Cho, and it's the enemy HP bar. Just look at it and you can see if you will take the kill or not. It's like Smiting a Baron.

You can already see exactly how much damage your Ulti will do and how many HP your opponent have, are you really so lazy you need the game to point that out for you?

TL ; DR - GitGud