And if these events truly are so large that they're basically a world boss in add form, then people would just form a crossrealm group to invite people, and treat it like another world boss.
I can't see any "dynamic event" that wouldn't be trivialized by the playerbase.
The problem is not that WQs are "repeated quests", original ones would become boring shortly later, too, and look at the minigames, original content, but often reviled.
The problem is that WoW at its core is an action RPG: "kill something, get rewards". This was already abstracted several times into variations of "interact with something, perform tasks", but anything really complex would clash with the MMO concept.