Wait, I thought this was a 3rd party showcase?
http://www.nintendoworldreport.com/news/54949/fitness-boxing-2-announced-for-december-4-release
Although today was a Nintendo partner showcase, a new Nintendo published game was announced.
Fitness Boxing 2, a sequel to the early 2019 release, will be available on December 4 with preorders open now. In North America and Europe the game is published by Nintendo.
Players will punch to the rhythm in this sequel which will have 23 songs to fight with, and save files from the original game will carry over.