[Update: According to this post at AndriaSang, Theatrhythm does have a story... sort of. It's something to do with the crystal of rhythm losing its shine, and heroes from various Final Fantasy games trying to fix that by increasing the music wave "Rizpo". Yeah. If you can make more sense of all that than I can, feel free to share in the comments.]
A lot of 3DS owners sounded a bit heartbroken when Theatrhythm was first announced. While the PSP gets multiple full fledged Final Fantasy games every year, the 3DS gets stuck with a rhythm-action crossover spinoff. I hope that 3DS owners are feeling less jilted as new details that come to light about the rhythm game in question, Theatrhythm Final Fantasy.
The game will have over 50 songs, 3 songs each from Final Fantasy I-XIII, and some form of experience point-based leveling up system. No word yet if the game will have its own unique narrative, but I'm guessing that Square-Enix will give us some sort of story to help string all the songs together. Also, word has it that the game was originally planned for the DS, but due to file size constraints, it was pushed to the 3DS. I've always heard that sound compression is one of the biggest challenges in creating a quality DS game. I'm glad that the 3DS is helping to change that.
Like many have said before, the music is one of the aspects of the Final Fantasy series that has remained consistently excellent throughout the years. I'm don't think we can go wrong with a game that focuses on one of the series's greatest strengths, while working to bring it to the forefront of the player's experience.