I think Box Boy is Nintendo published game, also it seems that Super Smash Bros. Ultimate 3.0 Update will be in April also (Joker will be launched before end of April), rumored Labo Kit 5 could be easily be April or May release and Starlink update is also April. Last year in May we had DKTF and Hyrule Warriors, so yeah, May look a bit empty, for now.
Technically it doesn't mean that we can't get further announcement for other titles in the period of April-May, but I'll admit that having no presence of Nintendo in that period might hurt them a bit ... until the EXPLOSION of summer that is !!
Anywoo, Box-Boy is an IP made by HAL so it was quite evident Nintendo would be the publisher, it's no Indie but a "small" release yeah.
Edit : Captain Toad Special Episode is in March ... there's that, I guess. (It's 6 bucks for the DLC)
March is OK, April is very strong in any case, but May looking a bit empty for now (but that could be easily changed):
-March: Yoshi's Crafted World, Final Fantasy VII, Chocobo’s Mystery Dungeon Every Buddy!, Unravel two, Captain Toad update
-April: Mortal Kombat 11, Final Fantasy X/X-2 HD, Final Fantasy XII, Dragon's Dogma: Dark Arisen, Darksiders Warmastered Edition, Super Dragon Ball Heroes: World Mission, Super Smash Bros. Ultimate 3.0 Update, Box Boy + Box Girl, Starlink update
-May: Team Sonic Racing, Assassin's Creed III Remastered, Atelier Lulua: The Scion of Arland