Sooner or later, we are going to have to see the ruined king in game
I don't know if riot will end up doing it as a PvE event or releasing him as a champ, but I feel like sooner or later they are going to have to get him in game for the players to interact with one way or another.
He's the cause of the ruination. The harrowing is because of the shadow isles. Multiple champs either serve him or want to kill him. He's got an item named after him so we know he should be a champ that wants AD, AS, and life steal. Releasing him would allow stories to progress. Even as an event it would be good for him to be in the game, but it'd be better if he was a champ.
I'm kinda of surprised riot hasn't done this already because it seems like it would have a lot of upside for them.