Replacing Grasp of the Undying
I think it's pretty safe to say that Grasp of the Undying has been pretty much fazed out thanks to Courage of the Colossus. There are just too many champions that have the CC to be able to use it, and on top of that, it's visually and functionally VISIBLE during teamfights. Your health bar has a giant freaking slab of gray shoved into it to absorb a shit ton of possible damage for the next 4 seconds. That feels awesome, and at the same time, not too overbearing for the enemy team (They can just not focus you for 4 seconds).
Grasp is a tiny bit of extra damage and sustain that goes almost completely unnoticed in the midst of a giant teamfight. I propose a keystone that rewards the tank/juggernaut who takes it for remaining the thick of things for so long. Here's my suggestion:
Grasp of the Undying -> Titan's Spirit
Every 1.5 seconds in combat, gain 1.2% damage reduction and increase in size. Stacks up to 10 times (5 times against non-epic monsters (No size increase when farming the jungle). Stacks fall off two at a time every 3 seconds
What this keystone aims to achieve is:
1). Being meaningfully different from Courage of the Colossus.
2). Bringing the meaningful visual and functional impact that Grasp of the Undying lacks but Courage of the Colossus has. (It is incredibly hard to not notice when the enemy team suddenly has a giant, and god doesn't that sound fun/awesome to do?