[Freaksken]

Creating the A.I. itself is not that difficult. The problem lies with the amount of npcs you'll need and the increasing combined system resources. In single player, when you go to say Las Venturas, the game will not create npcs in say Los Santos. It will only create npcs in your immediate vicinty, otherwise it would be very hard on the cpu, ... In multiplayer however, this approach is not possible (without clever tricks), since you have multiple players who can be at different places in the game. Say in single player the game creates 10 npcs around you wherever you go, it won't need more than those 10, which makes it easy to optimize the game around that. If you want to achieve the same experience in multiplayer, you need 10 npcs PER PLAYER (assuming they are in different places) which is increasingly hard on the server. More players, means more npcs. That said, it's definitely possible on a small scale though.