Yup, we did not forget about this among all the PS4-1 antics.
Search for 太鼓の達人 on the official Bandai Namco Entertainment site, and in addition to PS4-1 already taking two slots within the merchandise listing, you can also find this blank slate of an entry for a "Taiko no Tatsujin Series" Nintendo Switch game. But with no image, no CERO rating and no release dates (even vague ones like "Year 2017" from next door), it is next to impossible to talk anything beyond this. Enjoy the reassurance... I guess?
Thanks crystalsuicune for the heads-up from the Taiko no Tatsujin Discord.