Final Fantasy XIII was originally a PlayStation 3 exclusive, but ended up making the switch to multiplatform PlayStation 3 and Xbox 360.
Sister project Final Fantasy Versus XIII was also originally a PlayStation 3 exclusive, and has stayed as such since its announcement.
The various Versus trailers that we've seen since FFXIII's multiplatform switch have made it clear that the game would be PS3 only worldwide. But CEO Yoichi Wada was less firm on this stance during the Q&A session at an investors meeting today in Tokyo.
As reported at Impress Watch, when asked if it would be best to give Versus a multiplatform release on Xbox 360, Wada replied "We'll be looking into it internally until right before the formal announcement."
By "formal announcement," Wada is presumably referring to the proper unveiling of Versus. That's widely expected to take place at E3, although director Tetsuya Nomura has given some hints that the unveiling could come later.