I wish they would just call it FF15, but they won't because it will still carry XIII's themes, however they may be.
I'm cool if they go to PS4, because development-wise PS3 is nearing the end, and Versus has become too much of an investment to not use it for the next console.
Although Versus may be PS3's FF9/FF12, the last FF game to be made for a console of that generation. Which would make sense because the last game always shows off the specs of what the console can do.
But then again, we've already had 3 FF games on this platform already, 13, 13-2, and now Lightning Returns.