It's not that I wouldn't love to see this happen, it's more of a question of how it would happen. City Folk isn't really as relevant anymore, and I don't see Sakurai developing an easter egg that requires a 5 year old game (yes, time really does fly that fast) from a previous console to work. If there was a Wii U Animal Crossing, this would be much more likely.
I haven't played New Leaf - but how is the character memory stored? If it isn't like Wild World and is stored on the 3DS rather than the cartridge, they could potentially be transferred alongside the other connectivity features. Even so, it doesn't strike me as something that's really needed - as it's much less time-consuming for Sakurai to just model a handful of Animal Crossing villagers/the special event characters rather then the 80 or so villagers that can be seen in your town. It kind of reminds me of the pre-Brawl speculation that you'd be able to connect your Pictochat to Brawl to control the drawings on the stage in that while it'd be cool, it's extremely situational.