Have you ever gone to a living history museum? (Old Sturbridge Village is one example, my favorite I've been to). All these people in character, able to talk about the period, it makes for an amazing experience.
In traditional video games, if we try to or even accidentally push any deeper, we see the cracks in the universe. "Oh, I spoke to this person again, and they said the same thing to me." AI can help fix those cracks, and fill them in wherever the player ventures.
This certainly doesn't change Fortnite, but I think it could change immersive RPGs and MMOs.