This rumor is actually very credible. I would say that FF Versus has become FF XV. It makes sense, FFXIII wasn't well received, and they have already done multible spin-offs. People would give Versus a much better look if it was a new numbered title. Why waste all kinds of resources on what is aparently a unique and well-developed title by calling it a spin-off? Make it its own title.
The question then becomes systems and release dates. I think it will probably be on PS4. I think this was alluded to at the PS4 announcement converence. I don't think it will be exclusive though, or they probably would have announced it there. I think it will be on at least one other system. I think that system is probably Wii U, which would match up well with the leaked MiiVerse page showing "Final Fantasy 3". Square was probably thinking of WiiU having a solid intall base by the time the game comes out in both Japan and the west, as the Wii did. This would help them sell more copies than on PS4 alone, and they've had good success on DS and 3DS, and have DQX on the platform. The game may skip the XBox platforms, or may come there as well. Be interesting to find out though, I hope it's a real good game.
