With Lightning Returns: Final Fantasy out in Japan, Square Enix now is looking to continue to support the game via DLC costumes. Based on a video released recently, we can assume that the next DLC will be Yuna's Final Fantasy X-2 Costume.
As can be seen at the 2:24 and 3:37 marks in the video below, Lightning will be using Yuna's gunner outfit, with her weapon being Tidus' Brotherhood sword. With Final Fantasy X/X-2 HD Remaster releasing this month in Japan, it's likely that the DLC will be released sometime this month as well.
Lightning Returns: Final Fantasy XIII will be available on the 11th of February in North America, and on the 14th of February in Europe.