With next gen SSDs etc, I could get behind the idea of each player getting their own “version” of the gameworld. Sort of procedurally generated, but as a single, finished product. A world unique to you and your playthrough. We all get the same storyline/quests, but with different elements to them.
Some players get an ice world, others a fire-world. But that is their world, for that playthrough. You can jump/get summoned into other worlds by other players, maybe because you have abilities or resources from your world that could help in their world.