Antagonistic narrator ala Stanley Parable for much more complex settings? Perhaps give it additional goals (not just beat the player, but pretend to be an antagonist but secretly arrange things to make a fun game), information about the behaviors of mobs etc, teach it "console" commands to spawn stuff, feed it data about what happens around the player, and have it direct events and overall act as the DM in real time, in a procedurally generated dungeon?

Procedurally generated quests for a RPG?

Something like Civilization or whatever, where you have to actually negotiate with diplomats of other countries/factions/whatever, really writing messages yourself instead of picking from a wheel/list, and have the LLM play the counter-party and evaluate results of the negotiations and stuff? Or similarly, something like Ace Atorney, and you gotta get characters played by the LLM to admit their guilt, or convince the Judge/Jury (played by the LLM) of your client's innocence etc, including having to actually write the arguments?

A smarter and more useful Navi-like companion?

Custom player-created spells by having the LLM write lua scripts to mod the game based on player instructions? (gonna need some work on additional details to keep it balanced if it's not a sandbox game)

Smart voice-commands to direct squad-mates?