Right now, Minecraft is just for going online and building with friends. The survival part becomes boring after you explore everywhere. Adding trading with the NPCs would - although not stopping the "bore" aspect - at least add some more interest to the game. If they would build bigger villages, with the materials you sell them, populate them with new villagers, inherit "roles" if the current "role holder" dies, and maybe even create mines to get their own minerals, they would be come much more important, and something to be sought after. People now are just like, "oh it's a village." which is often followed by, "Lets blow it up/burn it down/kill everyone." I think villages should have a more important role in survival Minecraft and adding villages would be a great way to increase replay ability if even only by a little.
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TABLE WHY U NO STAY DOWN?
I'd seriously like to see that happen though(maybe in hardcore version?)
Well, it was aimed to be more of a joke, but the general idea was that they would spread at least until they reach a certain limit.
Also, why don't you add that Edencraft poster to your signature?