How would this be substantively different from Muds?
The big difference I'm arguing for is scope, and engineering.
If you have NPC chat bots that can learn, and an adjectives and typologies system for object, combine them so that chat bots can talk about objects adjectives and typologies. That sort of thing, really engineer the hell out of it.
In the end it would all be a massive NLP problem. As major advances in NLP happen the possibilities for MUDs is massive.
Not the same scope as DF, of course, but still surprisingly fancy. There's still a lot of room for more, though :) I'd personally love to see or make something like what you describe too...
I even started tinkering with my own home grown little MUD server written in Clojure, where I had intended to try out some fancy ideas... but lost interest because it would take a huge time investment and I'd be the only player in a multiplayer environment - maybe a single player game like you say would be better after all.