By this I mean we have a number of games that have procedurally generated levels, but none of these games seem to try to create a narrative that ebbs and flows as well. Generally the missions within the game take place inside a greater preset narrative.
For instance, in XCOM the general story beats of the experience of the game are preset but you have randomized missions thrown in here and there. People say "the gameplay is the story", and at times it is, but you still have preset cutscenes, preset mission dialogue, so on and so forth.
Another game that comes to mind on this topic is City of Heroes. There were procedurally generated stories in an essence but they were generally contained "one-shot" stories - some procedurally created gang might take over an abandoned complex, and you need to rescue some scientist and his research, blah blah blah. However, these one-shot instances weren't tied together into a cohesive story themselves - they were random disjointed events that happened across the city. The game DID have "campaigns" called Task Forces, but they were completely pre-generated affairs.
To me, this seems like the area that is the next leap forward. While you'll never get the quality of cutting edge pre-rendered cutscenes, and voice acting seems more difficult to pull off in such a system, a game that could continuously generate new stories seems like the pinnacle of infinite replayability... and yet I don't understand why we haven't seen attempts to tackle it. It is just that complicated?