Up until recently, Kingdom Hearts had mostly avoided basing levels off of new properties.
Because of this, the series has only scratched the surface when it comes to modern-day Disney. There are so many newer properties that can be tapped into for Kingdom Hearts IV, and they're going to need to start focussing on modern-day content, as most of the iconic older properties have already been turned into levels at this point.
When thinking of modern properties that Kingdom Hearts levels could be based on, it's important to establish that Disney is more than just the Disney Animated Classics. Whilst those have been the main source of inspiration for Kingdom Hearts worlds in the past, the Toy Box and Monstropolis have shown that the series is willing to adapt properties from other Disney-owned studios.
Also, a quick disclaimer: since we're focusing on modern content Star Wars won't be included, as if they were to make a Star Wars world then it would likely be based on the original trilogy which is far from modern.
Finally, modern in the context of this article is 2010 and onwards. If the property is a TV series then as long as the show ran past 2010 it's eligible.
Luca is easily one of the lesser discussed Pixar movies. It came out in the middle of the pandemic and unlike other Pixar films, Luca doesn't aim to change your life or anything.
Luca is a story about two kids enjoying summer together in the small Italian town of Portorosso. Nothing more, nothing less. Well they're also both sea monsters and the town happens to hate sea monsters but in comparison to what has been featured in Pixar movies beforehand, that's nothing.
It's a cosy movie set in a cosy town that would make for a great Kingdom Hearts world even if Luca isn't exactly the most popular Pixar movie.
This level could mix underwater and land-based gameplay in a way that the Pirates of the Caribbean levels could only dream of, as here Sora would be able to turn into a sea monster which would give the developers an excuse to make him swim really quickly. This would make the underwater segments really fun if done correctly.
When it comes to party members, Luca and Alberto would be great choices, and a finale where you race against Ercole Visconti would suit Luca much better than a regular combat-orientated boss fight.