One of the biggest things that makes Kingdom Hearts so lovable is its fantastic array of characters, both original and those crossing over from Disney and Final Fantasy.
Of course, new Disney characters are generally regarded as being more exciting inclusions - made pretty clear by the fact that we haven't seen any Final Fantasy characters appear so far (despite Noctis recently appearing in Tekken 7).
Although most Final Fantasy characters are relegated to cameo appearances in Radiant Garden or Twilight Town, some of them manage to have quite a big impact on the story - especially in the first and second game.
Saying nothing of just how excruciatingly hard Sephiroth's boss battle was in the original, hopefully the notion of making Final Fantasy characters integral parts of the narrative carries through into Kingdom Hearts 3, as they're one of the core aspects of the franchise.
Considering how long it's actually been since the last true Kingdom Hearts game, it'll be pretty interesting to see which Final Fantasy characters make a return, which appear for the first time ever, and which are left on the sidelines once again.