Their needs to be more to keep people playing for longer, after a while NL gets a little boring on non event days.
I hope the next game adds more interactive pwps that add things such as mini games, so one could be a tennis court with a tennis mini-game for example.
Also, bigger towns with more villagers and more players in one town, so like 8 player save files in one town, and people on your Nintendo network friends list can have a save file too.
one cool thing could that as you play, your character has their own personality based on player actions, kinda like the rumour thing in nl, so if you just doss about all day and never really make much progress, you become a lazy villager, your dialogue choices when talking to villagers will reflect that and you will get along with other lazy villagers more, and not so much jock villagers.
When someone else is playing on the same save file with a different playable character, the other playable characters will be walking around the town as if they are villagers and will have the personalities that reflect their play style.
It'll just make the game feel a little more alive.
Also a character creator in the beginning of the game, that way players can make their characters look more like them from the start, being able to change your hair colour and skin colour in the begging of the game as well as facial features, hight, weight and all that stuff.
Also I'm sure some people would love an option to play as an animal, it'd be fun to play around with the character creation tool making really cool animal characters and stuff.
Also, spot pass visitors, so villagers from your New Leaf town may pop round to your town (assuming the game is on the Wii U, most probably is)
Also more special events, more colourful and animated graphics style, being able to buy path tiles from nooks, being able to do landscaping (edit the terrain) grass that slowly grows over time and if it isn't cut will get really long and just look cool.
I have tons of ideas lol, not sure that many of them would fit in with the AC series, but I really hope Nintendo does something like the personality system for playable characters.