The studio responsible for Hyrule Warriors and Pokken Tournament on the Wii U has confirmed it has started development of an unnamed NX title. An analyst on Twitter last night tweeted the following:
KOEI TECMO confirm that they are starting development on Nintendo’s new console codenamed “NX”.
No project announced just yet.
— ZhugeEX (@ZhugeEX) April 28, 2016
So it looks like the train of developers confirming they have titles for the NX in the works will begin, now that we have a launch date for the console.