Sega have confirmed that Hatsune Miku: Project DIVA MegaMix on Switch will release on May 15th in NA exclusively on the Switch eShop as a digital-only release. Players that pre-load the game will also get theme song pack DLC for free on launch day.
According to the Australian eShop (spotted by ggx2ac on ResetEra), there will also be a deluxe edition that comes with the 6 song packs of DLC. And there’s even a demo available there, so it’s safe to say both will apply in NA as well. The game will take up 13.8GB on the eShop also.
Gematsu has a great collection of articles to refresh you on what’s in the game. You can read these articles here, here, here, here, here, here, here, and here.