Originally Posted by
Kirin
9's story works wonderfully for what it is: self contained stories about 8 (9 if you count Beatrix, Zidane and Kuja count as one story) characters challenging how they perceive the world around them. Expanding Beatrix into before Queen Brahne was corrupted or Garnet/Sarah after she fled from Madain Sari are cool individual character development episodes but not enough to carry a game narrative for 40+ hours.
X-2's story did have only 3 real main characters, but two of them are already known and pretty deep and the third is expanded on fairly well through the course of the game. It helped that X's presentation really developed the emotional impact of it's ending, and if the game was on the PSX I don't think it would be as well regarded as it is. That let X-2 get away with a smaller cast as the narrative was already hyper focused on Yuna and fixing what she lost after restoring what Spira lost.
I can see 8 of all titles getting a working sequel in game form. There is a lot there to deal with regarding the descendants of Hyde and what happens to the Sorceress now that Rinoa is the last of its line. But even then they gave everyone in Garden a pretty happy ending and wrapped up that narrative with a bow so that might be a hard stretch to revist unless it gets a little campy with "Well guess what guys, Ultimecia is back and shes MAD!".
tl;dr sequels generally suck from a narrative perspective if the original game did a good job, and whats the point of said sequel if the narrative did do a good job? X was an exception because of its presentation and built in story elements, but not enough for a playable X-3. Stick to the light novel SE.