Agreed.
Ultimecia in KH3? It would be cool to have a FF villian aside from Sephiroth appearing in the game
I can see the writers setting up the Balamb Gardens as a separate district (perhaps simply called the Balamb District) in Radiant Garden. Ultimecia can possibly appear somewhere over there and it is in that location that you can have a boss battle against her. That being said, I'd kind of like her to be part of the story as well. The Cloud/Sephiroth subplot was a decent enough attempt, but they could have handled it better.