Honestly, I really think it's inevitable that Final Fantasy XIII-3 will become official very soon. The evidence is all right there, I say.
Therefore, it's accurate to call these FFXIII sequels a mini-series of sorts; a series within a franchise, if you will. But we've never really seen this in the Final Fantasy world before; we had FFX-2 (but no FFX-3) and even then, main character Tidus wasn't playable in the sequel. Only Yuna and Rikku returned, along with new character Paine. So the question is this- Is Lightning a popular enough protagonist to have the staying power?
I mean, I usually try to have my finger on the pulse of FF nation, and I'm not sure any die-hard fan of the franchise would place Lightning at or even near the top of their "most beloved hero" list. She actually annoyed the crap out of me in the first half of FFXIII, as she seemed completely one-dimensional to me. She did, however, get a lot better in the second half, although I still found it odd that in many respects, it could be argued that the true heroine of that game was actually Fang. That being said, Lightning was much better in FFXIII-2.
She wasn't even playable (unless you took her down in the Arena or you got that Lightning DLC) but at least she was more of a bad-ass; she was a goddess, for crying out loud, and she really sort of came into her own. The story wasn't fantastic, unfortunately, but the character of Lightning did take a few necessary strides forward in terms of solidifying her role and personality. But this is just me; does the rest of the FF fanbase really want to see Lightning again in a new title? Or are they going, "hey, if you want to make a sequel, make freakin' FFVII-2 and bring back Cloud!"
I admit to being a much bigger Lightning fan now than I was after FFXIII. I'm just not sure if others feel the same way.