Monster’s Inc. is actually the best choice you could make if you wanted to add a Pixar movie other than Toy Story to Kingdom Hearts.
I mean, Up and The Incredibles are way too close to just being modern human worlds, Ratatouille is not as adventure-y, Brave and Finding Nemo are too similar to stuff that’s been done in KH (medieval fantasy and the ocean), Inside Out and WALL-E would require way too many explanations to be handwaved, A Bug’s Life and The Good Dinosaur are not as popular and Coco came out too recently.
Cars could work, but Square Enix knew that’d be a bad decision.
Why is Cars is a bad decision? It’s popular as fuck and I would love a Mario Kart style racing mode with magic for a power-ups. Also, imagine Goofy as a pickup truck.
As for Inside Out, I think it’d be easy to implement.
Yuffie or whoever the fuck: “This is Riley, she’s in the process of becoming a Heartless, but you can prevent this by entering her mind and fighting the Heartless infection.“
With Inside Out, Riley’s a normal human person from modern-day San Francisco and the levels would be based on the mind of someone who grew up in that world. It could happen, I guess, but it’d be the most grounded, normal element to ever appear in Kingdom Hearts. I don’t know how if she’d fit well with the universe.
And with Cars, it’s Cars. It could work, but it’s Cars.
Did you even watch Inside Out? The inside of Riley’s mind is a fantasy-like realm full of bizarre locations like a dream factory, imagination town, and a subconscious cave of monsters. It’d be right up Kingdom Hearts’ alley.
Aesthetically it could work, sure, but narratively it would require a lot of compromises.
Inside Out is ultimately a movie about a kid who is moving to another town and is trying to cope with the changes in her life. Yea, it’s told through a very fantastic lens, but it doesn’t actually have fantastic elements in it.
Like, Tarzan didn’t have any overtly fantastic elements in it either, but it took place in a jungle and had animal characters. Inside Out didn’t even have that.
And while the locations are bizarre, they’re still gonna be based on the mind of a very grounded character. Like, her dreams are about going to a normal school, her memories are of her being in a hockey team, etc.
A Bug’s Life would have been rad, though. I wish we had that, too