Maybe some sort of AI-powered D&D DM; the rules of the game would be hard coded, but the AI would determine how the rules are applied and how they fit into the story based on text input from the players, results of dice rolls, etc. (E.g. If the AI were to end a sentence with "Roll for initiative" then the hard-coded bit of the game would have everyone roll initiative and feed the results back into the AI.)
You: I kill all of them and become an immortal god.
Game: No, that doesn’t make sense. You can’t just kill everyone; you can run over and attack them, and see how that goes for you if you like...
Without constraints it’s not a game, it’s just telling yourself a story.
...nothing wrong with that, it’s fun. ...but it’s not a game imo, any more than giving someone a blank piece of paper and a pen is a game.
e.g.
Kill troll with sword could be submitted as either "I have a sword, so kill troll with sword" and "I have no sword, so kill troll with sword" That's obviously very hand-wavy but it would allow a more stateless setup.
I have been planning on writing a sci-fi epic for years, as you do. It's very nice to bounce half-baked ideas off the AI just to see how it responds. I would not subject a human to the cruelty of my whims in this way. People largely prefer the safe response of logic and understanding, even when I mischievously have presented them with nothing of the sort. The AI responds with chaos and creativity.
It seems to actually learn and I have taught it about shrink-ray guns, which it seems to make appropriate yet unexpected responses to. At first the shrunk items just disappeared. Then the ray-gun's charge started running out. Later, shrinking the place the ray gun was in caused paradoxes. Eventually the shrink-ray actually made things shrink, but putting my space ship in my pocket transported me across space and time to a desolate, ruined place. I decided this was a poetic way for it to tell me it did not know how to continue.
The AI is a free-form role-playing partner with a delightful lack of tact, but it is not immune to reason. If one can suspend disbelief and fill in the blanks it is even barely intelligent.
Don't get me wrong, it's cool as hell. But it's getting tiring hearing everyone trying to spin obvious flaws as innovation.
If you expect this thing to be a MUD or roll-playing game it's not going to meet your expectations. 'Text adventure' perhaps sets the wrong expectation and in that regard I agree with you that it falls short.