Looking at all the Final Fantasy games out there right now, I can't really think of a world where I'm going "I wish they could expand on this and make a new story".

I do like the spin-offs though. I highly enjoy games like theatrhythm and dissidia. I wouldn't mind more games like these where you can go back and revisit your favorite characters and settings without messing with the canon of the series.

Games I would like: A simulator where you can create and pilot your own Garden, not to mention the Blitzball 2K14 everyone likes to talk about.

But I liked Crisis Core, XIII-2, etc. I'm not against a prequel/sequel idea, I just can't think of any where i'm actively wanting it. Although I've always enjoyed the idea of an X prequel where you go through Braska, Jecht & Auron's journey.