Say you prompt GPT to think of something different that happens, given a description and time of day.

You can keep all of the stuff like multiple users interacting with each other. You can also have an automated interface for admins to add on to the world. And it might be even easier to recruit people for that because you would have the AI to check what they were doing for quality and style or plot consistency etc. and fit it into the system, even automatically translate some mechanics or parameters into code.

Part of each prompt for combat or something would be the player stats and inventory. It could also have commands like "roll dice" or "next combat turn" etc. People can talk and interact. With GPT4 especially it should enable new possibilities, like custom encounters or areas that are designed on-the-fly for an ad-hoc group.

I think that an integration of GPT4 with things like MUDs has incredible potential.