I would love to see NPCs added so if people dont feel like playing multiplayer they dont have to. And you can run your own government without online players who may mess up your world. Just an idea :)
OPTIONAL NPC's, Something that can be turned on or off when a game/server is set up, In my opinion, would be very good for small servers with few people or for those who are playing alone. Have NPC's perform specific jobs and sell and trade their good to the player or players in the world, perhaps something where the players would have to build houses to "attract" NPC's to the area and then the NPC's could build their own "workshops" onto the house.