Was waiting for a thread about Zoro COO.
It's pretty obvious though, Zoro's last haki to bloom is COO and it is gonna happen in the Shiryu fight.
Mihawk is a very calm and collected person, also a very observant one. Given his name "Hawkeye" and "Clairvoyant", which was what Oda originally gave, most likely have advCOO.
Zoro aside black blades, needs to bloom his COO in order to matchup against Mihawk.