I think AI should be handled by the game and not the engine.
Take for example a flight simulator using the engine. Users would expect the following:-
1) Aircraft following real world schedules
2) Real world liveries
3) Accurate ground handling of aircraft (eg wait for landing plane prior to crossing runway etc)
4) Accurate departure (SID) and arrival (STAR) procedures
5) Ground vehicles (fuel trucks, baggage carts etc) and ground handlers at airports
6) Passengers in the terminals and visible planning/deplanning
7) Aircraft/ground vehicles using lights/reversers etc as appropriate
The flight simulator could handle all that assuming the engine provided the following capabilities:-
1) Create an object (plane, ground vehicle, passenger etc) at a specific position XYZ (ie lon/lat/alt ASL)
2) Delete an object
3) Give object a waypoint (eg move to XYZ at given XYZ speed, accelerate to that speed at given XYZ rate)
4) Query list of object variables (eg lights, reversers, flaps, doors, etc)
5) Query state of a object variable (eg are lights on or off)
6) Set sate of an object variable (eg set lights on)
7) Query list of objects within given radius of XYZ (eg get list of all planes within 25 NM radius of my airport)