Zoro realizing his sense of self and consciously infusing his swords with Conqueror's Haki is the first step toward being officially acknowledged as the Vice Captain. Zoro is already known throughout the world as the No. 2 of the Straw Hat Pirates. That's nothing new, but I think his post-Elbaph bounty poster could potentially include "Vice Captain" as his title, alongside Dai Kengo (Great Swordmaster), instead of just Kengo. I already made a post about this in the past (linking it below), discussing the potential situation regarding Barto. The Red Hair Pirates destroyed the Barto Club. Even though it was Barto's fault, and he himself said that it had nothing to do with Luffy and that they chose to follow him on their own, they are still part of the Grand Fleet of a Yonko crew. If Luffy does nothing about what happened, it could be seen as a sign of weakness. I think this is where Zoro will step in. When Shanks and Luffy eventually meet, I think the Barto incident will come up, especially since the Straw Hats have already read about what happened. Luffy may be unable or unwilling to confront Shanks over it, but Zoro will, and we might even see a clash between the two.