There was apparently an ambiguous ending to XIII-2 that implies more might be coming. I didn't pay much attention to the story since I didn't play the game, but it did bother me that they would consider ANOTHER game in this universe and not give us an HD remake of VII. As much as I love Lightning (and for the record, despite my general dislike of XIII, I do really like her), I just don't think her story merits this many games.
I'm not even sure what I want from this franchise any more. It's given me so much over the years already, and given the fact that the stories are unique to each other (unlike Metal Gear Solid, for example) it's downright amazing how many of these games I've loved. Do they have any more great original ideas left for stories? Can they tweak the gameplay to make it even more fun? I really don't know. All I can say is, since VII (their undisputed most popular game, even if you want to argue against it being their best), the games in the main sequence have been very hit or miss to me. I didn't like VIII (poor characters, didn't like the junction), X (voice acting... "yes"), or XIII (again, characters bothered me, especially when they were forced on my party). I thought IX and XII were both excellent.
Given that track record, statisticall speaking, I shouldn't expect much from XV, but I would still buy it if it came out tomorrow. I think I'd rather see a remake of VII, but whatever. But I can understand if they don't want to risk ruining its legacy with something half-hearted (like Lucas and all his stupid Star Wars tweaks).