I’m having trouble finding a source on this, but I recall Square Enix stating a couple years ago, during production of Theatrhythm Final Fantasy, that the Theatrhythm title was not necessarily exclusive to the Final Fantasy brand. Now, two and a half years later, they have officially confirmed that tease to be true, announcing next year’s follow-up to the musical series: Theatrhythm Dragon Quest.
For now there is merely a teaser site which showcases the game’s logo and a handful of in-game monster designs, but they have promised to reveal a proper trailer at next weekend’s Jump Festa event, happening in Chiba, Japan.
Theatrhythm Dragon Quest is slated for a Japanese release on March 26, 2015, exclusively on the Nintendo 3DS. History would indicate a western release is likely to follow around midyear.