A co-op game set in a open/sandbox fantasy world that is truly alive, driven by AI. You can do as you wish, join a Kingdom as a soldier for example, set up a village somewhere maybe. Become a trader. Hunter. Whatever you want. The ultimate open survival game I guess.
But the key part is behind the scenes an AI will change the story of the world as time passes. Perhap on the other side of the continent a war wages between 2 factions that threatens to pull the whole region into termoil. Maybe you'll hear about it from a passing traveller. Maybe you won't hear about it at all and the next time you go travelling far and wide you realise a new Empire is rising.
Perhaps the AI decides to slowly bring about the collapse of society through climate change. Perhaps you become embroiled in a plot to assinate a King. The AI decides all the variables, you can only react to them, maybe you can try and change the story with your actions.
One day you are out hunting and you see in the distance an army marching to war. Maybe you decide to catch up and join the army. Or maybe you'll hide and hope that wherever that army is going, it won't come to your neck of the woods.
The AI continuously evolves the world around you to keep things interesting. Every game will be completely different.
It'll probably never get made, it is massive in scope.
I think this will happen in a decade or so. We have stuff like AI dungeon now, so people definitely want this (even though most people use it for sex stuff currently)
I have the same desire. It would be awesome to play a co-op D&D campain with an AI dungeon master in a living world. It generates quests and scenarios on the fly, keeps track of your actions, always able to adapt to the changing landscape.
Yeah, you obviously can't code for infinite possibility, so it just has to be robust enough. And the first step would be text-based. "I walk into the tavern" "There's a fight happening / it's now owned by someone else / bartender asks if you want the usual" kind of thing. Biggest hurdle is having a persistent and cohesive world.
Given the advancement of image/song/code generation, I think it's not out of the realm of possibility for a game to be truly limitless. Just not remotely any time soon.