Cadence of Hyrule is due out Spring 2019. With Summer kicking off June 21st, 2019, there's not much time left for the game to launch. While Nintendo is yet to announce an official release date, dataminers think they know the answer.
Just a few hours ago, dataminers noticed that the Switch eShop metadata for Cadence of Hyrule had been update. That update included a date of May 30th, 2019. That obviously has lead dataminers to believe that May 30th will be launch day for the title. That falls perfectly in line with Nintendo's usual eShop updates, as May 30th is a Thursday. I guess we'll find out if the metadata is spot-on soon enough!