As we have known and felt the indomitable conquerors haki of Luffy, even while unconscious. Luffy being a prodigy hakiman, and his natural tendency towards CoC haki, the elemental CoC haki seems the next big upgrade. Yes, he could learn more about adCoC from shanks himself and even surpass him with further breaking the time and space barrier.
"Will of D" is something that needs to be explained why the world government are so afraid of.