Depends on if he awakens all swords at once (fairly unlikely in my mind) or gradually. If it is all at once it will be against Mihawk, if it is gradually? Could see him awaken it against Shiryu, "Ghandi" or Kizaru, and Mihawk. Mihawk likely being the one to turn the final blade black, and it should probably be Wado thus fulfilling the promise to Kuina.
Could see this getting further celebration if we get a full-on Elbaf focus next arc instead of immediate endgame since the giants knowing a thing or two about the weapon and their final states via turning black permanently would make sense. Some Odin characters having a black spear to represent Gungnir or a Thor character having a black hammer to represent Mjolnir could work.