The question is - will it be a card game? A dress up/home deco game? A dress up/home deco card game?!
This will be interesting.
On the one hand, the Animal Crossing formula would fit very well in the mobile landscape; it has a social/communication aspect; it has plenty of collectibles; and a structure that can be quite well translated into a F2P w/MTX. Also, it is a small game in terms of scope, that is, the village has a nice size and everything can be condensed in mobile format without losing much (unlike an open-world, for example).
On the other hand, I do not think Nintendo would like to create a game that is too similar to the console counterpart, as long as the latter is wildly successful (5m+ in Japan, 11m+ worldwide). It seems that Animal Crossing has a quite faithful fanbase that is willing to buy the game at full price as it is, maybe with some improvements here and there. A mobile game in the same genre and structure would compete too much with the likely Switch version. This, of course, is true as long as Nintendo is developing a console episode as we speak, and it is planning to release it in 2018.
An aspect that might differentiate Animal Crossing mobile relates to online functionalities. The game might be a MMO-like life-sim, where villagers are real friends or people met online. In this way, even with the same game system, the mobile app would skew towards social features, while the console version can retain a more traditional structure (it does not have a story, but it still has characters and small vignettes).