Tommorow Land

[WhiteArchmage]

There may be huge copyright issues in place: outside of his game, I believe Sora has only appeared in Brave Exvius as a limited time unit, and no other KH characters because all original characters for KH are actually owned by Disney. While there's been cross-overs between companies before (Monster Hunter and Yokai), I don't think the mouse would be very open to having some of their Disney characters show up in XIV. Characters like Sora, Kairi and stuff like Keyblades, maybe... a very distant maybe...

Also, given the large stylistic differences between the games, I shudder to think how they'd translate Sora to Eorzea... at least the Yokai had some excuse to remain cartoony.