I have been waiting for years for an AI model like this to be implemented... A friend and I were going to create a game once upon a time, and I had fleshed out the theoretics of putting such a model into practice. Its not impossible from a logistical standpoint - and on the scale of a game like STALKER it shouldnt be that hard to nail down. No, im not a programmer so I really have no clue about the coding involved, but from a design standpoint it is immenently feasible.
The original idea I had was to create a model like this for an entire world or region, and to have the scope of a few generations of time. It would have been a low-tech fantasy type world (because you have to cut corners somewhere if you are going to obsess on detail) A database could hold relevant data pertaining to each spawned entity, which would be tracked purely by numbers and stats until the player came across them. I got pretty technical with the various details of life, power, motivations, quirks, etc. etc., but quickly came to the realization that such a game would have to be entirely unscripted from a situational standpoint. This created further details in terms of npc interaction. But overall, I think it could be done. The end result would be more like a simulation than a game per se, that is unless you could get the NPCs to make the storyline for you. That was what I had been working on when my friend decided to go work for Coca-cola instead. Cest la vie!