I was wondering this during my last game play, and I do believe there's more room for AI activities to improve.

To start with, I roughly observed the major activities of every existing AI driven NPC, and to be honest, I found it quite odd as a human, that those NPCs does not actually do anything related with current in-game time, something like sleeping during the night time, periodic showering everyday, or merely just go to kitchen to get some water, etc.

It appears to be more obvious when playing the "free discovering mode", that automatically cycles the day and night during the game play which makes a wonderful scene to watch that one of those NPCs playing his piano, alone, in his bigass hall, at the time of 2 in the morning, while he has a giant bed placed upstairs in his bedroom which, according to my observations, hardly used by him but only for players to bounce on it.

What I mean is, some of those static environment items, such as furniture, could be designed to be utilised and made connected with those NPCs in order to create more activities for them, and they might just have more realistic daily routines as well.