Back in 2010, Nintendo filed a patent application for something called a "massively single-playing online game," something whose interactions don't take place in real time and what sounds a little Animal Crossing-ish (above).
According to GameSpot, which found the filing, the MSO(?) would be an environment where players' actions and choices affect the world they and everyone else inhabit. Economic systems are a good example, one Nintendo used in the filing.
In one case, if a player finds building materials and constructs a house, all other players would then see that house, just not its owner. Nintendo also described a concept where players gossip to an AI non-player character. who then spreads it to others in the world.
Finally, if players "friend" one another, they can see and interact with them in the same environment.
One other thing, the filing describes the game being suitable for play on something called a "Wii 3D system." This was filed last year, before the 3DS was known. While the term is eye-catching, its quite possible its either a mislabeling, our outdated information made non-operative by the 3DS and/or Wii U. It could also be legit, but this is hardly confirmation of that.