My idea of an ideal Kingdom Hearts game does indeed feature at least a couple original songs. Utada writing all the songs would be amazing, and she could even voice a character who sings in both the Japanese and English versions of the game. If not her, getting Alan Menken to contribute would be something. Maybe even Danny Elfman, you never know. Or someone like Lana Del Rey, who's worked with Disney a few times now and does a lot of original songs for soundtracks. Shimomura does not sound like she enjoys writing vocal numbers very much going by her interviews, that's why I'm even mentioning anyone else.
The game I'm imagining is, let's say, a new worldline reboot, so different voice actors and a story that stands on its own like a fairy tale. There should be at least one boss who sings while you fight them, like Ursula but scarier and not a minigame. Riku, or the equivalent rival character, needs a tormented heartbreaking ballad.