I can't see 'Animal Crossing' happening in this Direct. A Direct made in September is intended to market and rise visibility for the games launching in the last quarter of the year.
And 'Animal Crossing' is a game as anticipated that if it's presented in this Direct, it will cannibalize all the attention. The only talk will be about this new 'Animal Crossing'.
A Direct is intended to generate buzz. They have games released in the last quartet of the year that they need to sell, they need the fans talking about these games and making pre-orders.
And there is no way in which 'Animal Crossing' is a 2018 title, because this is among the 3 most important IPs for Nintendo. They will not start promoting the game as late as in September.
So if it's a 2019 release, an announcement will not happen at least until December, in a best case scenario, if it's intended as a Spring title. Once the Black Friday has passed, and once 'Super Smash Bros Ultimate' has been released.
If a single title releasing in 2019 will appear in the Direct, they will be niche games that really need to generate a talk, obtaining visibility in the long term, because they are less anticipated titles.