I think FFXIII-2's numbers have a lot more to do with home gaming shrinking in Japan than everything else said here. I think the major changes happening in the habits of japanese players will be a real problem for all the devs there, Square Enix included. And Final Fantasy is part of it. Being a saga loved everywhere at the same level, they're loosing fans in Japan by insisting on developing it on home consoles when everything else changed in the landscape; at the same time, in the west home gaming is stronger for this genre and type of games. What will happen to FF? Will it become a multiplatform title with a focus on portables for local market and home consoles in the west? (PS3/VITA for example) Or will they drop the interest in Japan and try to make the saga stronger in the west?
The changes we will see after Versus's released will be BIG. I'm not expecting FFXV at this point to be on home consoles anymore, or not just on home consoles. Japan wants FF on portables like they wanted Monster Hunter and then Dragon Quest. Everything's changed, Square Enix will have to adapt.