A rumor started by Destructoid, this one. Says Nintendo is using a demo of a new 3D enabled Animal Crossing to attract 3rd party attention to it (the kind that is less likely to churn out terrible games, I hope). Dtoid's reliable sources say that this will be revealed together with the console itself this E3 too. Whatever happened to Mario spearheading every console launch?
It's all just speculation though, but if it turns out to be true, Animal Crossing's got to do way more than just tack on 3D effects to the existing Wild World game to truly capture any attention. City Folk was just a lame cash-in and an excuse to release Nintendo's less than stellar voice chat option (Wii Speak).
