I think I've seen this thread before and I'll say now what I said then:
Zilean doesn't work as a mage king. It's not in his personality. He's a scholar, an academic. He also can't have been one of the mages who helped unleash the Void, because he would have died immediately in the battle for Icathia, like the other mages who were immediately consumed upon opening the tear.
Zilean is a scholarly mage, and he needs to remain as much. He's slightly aloof, isolating himself in his tower for his research, and so he technically could work as being a wielder of a world rune, but overall, he's generally avoided conflict over the years, kept his nose clean, and not endangered himself or his work by partaking in war or politics. He can be just as engaging as a character to fill the hermit mage trope of a powerful, well known mage who lives on the fringe of society in a hard to reach place - he doesn't need to have conquered kingdoms or opened holes to other realms in order to be an interesting character, and quite frankly, we need more simple, interesting characters in the game. He's also fairly lighthearted, and anything like politics, war, or the Void would greatly detract from him as the jovial mage he is.
He desperately needs a VU though, and probably some level of GU as well, so I'd say more along the lines of an Ezreal level VgU than a Morgana level VgU.
