I'm assuming don't bring him to life, game wise.
But for a writer standpoint, imagine how horrifying that would be for Yasuo. Hear me out.
Say in some twisted scenario, Yasuo ends up in the Shadow Isles, maybe with someone else accompanying that we know or whatnot.
Both get themselves stuck in a situation that has them cornered and makes them see the worst possible things they could see.
For Yasuo, it would be Yone's grave at first, just nothing but him and that grave. Yasuo watches as a hand bursts through, and a revenant or half-skeletal Yone bursts out of the grave, with very graphic and horrifying details that give off this zombie, nightmare version of Yasuo's brother.
Nightmare/Undead(UD) Yone could go off to say as, "Why didn't you avenge me, brother? You haven't kept your oath, and now you're coming with me."
Yasuo ends up having to fight UD Yone in a battle, ends up getting beat, Yone's about to kill him, but then Yasuo's broken out of it by the other person he was accompanied with, they end up fleeing out of there, who knows, maybe meet up with Lucian and Senna, I don't know.
Just thought this would be a good story idea, criticize me if you'd like.
But for real though, don't bring Yone to the game and/or as a playable champion, he could have more narrative potential, but leave him out of this.