How freaking ******** are you people? Why would Sakurai and his team bother coding something into the background that would just be removed? The roster was already done long before the update, so this is a plausible argument. Anyone who disagrees just isn't thinking it through.
To have as many Animal Crossing characters as possible with little work? The answer is said simply by looking at a few screenshots of the stage. If you couldn't come up to that, I guess you just aren't "thinking it through". It can be summed up to as little as a True or False value. If it can get more characters in the background, do it.
I'm not pro Nook, but that's a horrible attempt at trying to making your view sound supreme while making any other view sound like little thought was put into it. The irony bothered me enough to post.
Edit - In defense of the Animal Crosser, look at the screenshots in today's update;
In many of them, you see two Animal Crossers of the same gender in the background, and other times of both genders. What does this mean? This means the developers don't mind more than one instance of the villager to be playable since he or she doesn't really have a set in stone identity, just the human characteristic. So while I really, really doubt Nook will get in, Animal Crosser is still quite possible.