In recent expansions some areas are “time zoned”: one can pick the past or the present to play in, like the Blasted Lands.
Why not do this for every area? Such as Felwood before it was poisoned, or what it looks like now, and offer quests in these areas.
Not world quests, in my mad vision war boards would be used again. It would list the quests for the past and present, and accepting the quest will time-zone the area and make it match one’s current level for a greater challenge.
Azeroth and Outland have so much more potential than a timewalking dungeon event. The story doesn’t have to end with the next expansion. Why not make use of the content we have?