As much as I liked the AC plaza's graphics and New Leaf's graphics style, I kinda wish AC would go for a more colourful art style, maybe take a note from Wind Waker HD and do a nice cell shaded look, basically I just want the game to look like that anime movie.
Camera control is a given, it can really help with the immersion.
Fix the grass decay, seriously, if they must keep it, at least make it less destructive.
In fact, one thing I'd like to see, and I've posted this before but whatever, grass that actually looks like grass instead of a green texture, and over time, it will grow longer, so if left alone, it can get quite long and will just look cool (obviously can be cut somehow)
Also that could work for the players hair as well, so at the beginning the player gets a little more choice on the way their avatar looks, stuff like hair, skin colour, hight, weight and so on, makes it a lot easier to get into a game if my avatar looks like me.
But the players hair will grow over time as well, and once Shampoodle is unlocked, they get to style their hair rather than pick it from a list or a questionnaire.
Bigger town with more villagers (16 like the original) and players get more control when customising it, so no main street, the shops are all in the town, and the game could have a feature like Harvest Moon a new beginning's edit mode, where players can move all the buildings anywhere, they can lay down paths, and lot's of other cool things, although this being Animal Crossing, moving buildings would be an overnight thing like with PWP's
More interactive PWP's and just more to do in a play session, this is a console game, players don't want to boot up their console only to play the game in short bursts like NL, their needs to be more to do, more detailed conversations with villigers (sort of like Mass Effect convos with lot's of different dialogue options and stuff) interactive PWP's that add minigames, such as a Tennis court or an arcade with GBC games or something.
A better online focus is a given, the Wii U could bring a lot to the series, such as sharing a town with a freind online (the town being saved on a server, and is updated when a player saves, when two players play the town at once, they can play together like standard multiplayer, how cool would it be to share a town with a freind who doesn't live with you IRL?)
Nintendo NFC support, these can add so much to the game, when I was a kid, the E reader seemed like such a cool idea, buying something from a shop that adds things to the game (in AC, there were NES games and stuff) sadly the e reader was a bit rubbish and never made it to Europe, but Nintendo's NFC could do the same sort of thing but better.
They could sell models of new PWP's that aren't in the game, that once activated, will unlock the PWP, it could also be used for exclusive furniture and even villigers that can only be accessed through owning their NFC figure.
Some would say it's a bit of a rip off, but it has so much more value than standard DLC, you're not just buying a digital add on to a game, you get something that you can physically own.
Also using ones such as the Mario or Zelda figures can replace the fortune cookies and give lot's of new items.
The NFC figures could make Nintendo so much money and are just a perfect fit for Animal Crossing, it could also make finding dream villigers a lot easier, being able to go buy a little toy version of them, scan it on the gamepad's NFC sensor, and then the next day have them move in, provided there's room in the town.
It worked a charm for Activision's Skylanders series, and unlike Skylanders, which wasn't that great a game, and required an expensive add on, the Wii U has a built in NFC sensor on the game pad, and also has Nintendo's know how.
tl;dr Nintendo NFC= money for Nintendo + more lasting value to gamer than DLC