Level-5 have announced that Ni no Kuni 2: Revenant Kingdom will no longer be coming out in 2017. Its release date has now been pushed back to January 19, 2018.
"We have decided that more development time is required in order to deliver the full Ni no Kuni II experience to our fans,” Akihiro Hino, CEO and president of Level-5 says in a press release. “I deeply apologise to those who have been looking forward to the game's release. Please rest assured, however, that we will continue to strive to provide a deep and satisfying single player experience that our fans can look forward to enjoying.”
Still, at least this means you have time to play through the first game again ahead of the sequel's launch.