The Director of Final Fantasy XV, Hajime Tabata, has been busy working on "expanding the universe" of the roleplay with Ignis and PC porting, but also has a new project that we will hear about next year.
In the last issue of the magazine Famitsu, Hajibe Tabata said that "He intends to start seriously working on a new project from next year."
He also added: "I want to face a new challenge that will allow me to further expand my work on Final Fantasy XV."
Tabata has already said that he would like to give players a similar experience Breath of the Wild for his next project, but since then we have not heard of it anymore. Anyway, we'll probably know more about it after the release of the PC version of Final Fantasy XV at the beginning of 2018.