Tetsuya Nomura, famed character designer for many of the Final Fantasy and Kingdom Hearts games, said previously that Theatrhythm Final Fantasy would include DLC, but now there is tangible proof.
The Japanese box confirms that there will be paid DLC, as well as evidence of something called the Nintendo Network.
This is all news regarding the Japanese release of the game, but it's a fair assumption that a North American version would have comparable features.
For more about the easy to spell Theatrhythm Final Fantasy (I didn't have to look up how to spell Theatrhythm because it's such a normal word), check out Tim Turi's hands-on time with the game here.
[Update] In the interest of clarification, a North American version of the game has not been announced. To have the game here in the United States is hopeful thinking on my part.
[via Andriasang]