Theatrhythm Final Fantasy: Curtain Call will not only incorporate songs from the previous version, but a mode only found in the iOS port as well. The "Quest Medley" mode will reportedly be included, a feature that wasn't in the original 3DS release.
Quest Medley let you select random songs from the music catalog and string them together to make quests. 4Gamer (via Polygon) reports that the Curtain Call version of Quest Medley will also let you build your own routes with the choice of short, medium, or long quests. You'll also apparently be able to share user-created maps with other players.
As previously reported, producer Ichiro Hazama thinks that Curtain Call will be the final Theatrhythm game, and to make it a complete experience he's trying to squeeze in songs from the entire Final Fantasy catalog, including the ones in the previous game. He said he's regarding the old playlist as a base, and adding new ones on top of it to "try to get as close to a complete song list as possible."
Curtain Call is due in Japan sometime this spring. A North American release has not been announced.