Some worlds are more suited for a point A to point B adventure, like Monstropolis, others are more suited to slightly more open design like Olympus, with the large city and mountain with branching paths, and then some rare exceptions work like Caribbean, with a large world containing islands with somewhat linear exploration on them.
What won't work, I don't think, is large, fully open worlds that you spend a long time in. Kingdom Hearts is a game that's fun to play over and over again, and I think overly large (to no benefit) areas can hamper that breezy sense of replayability. Sure, they've flirted with bigger and bigger worlds, but the content spread itself is relatively the same across all worlds. Caribbean has a lot of islands, but none of them are massive-- You can consider the ship sailing a simple minigame that takes place in-between islands.
As far as a massive city like Quadratum goes, I remain unconvinced of the Kingdom Hearts team's ability to make the scope feel meaningful AND fun to explore. In KH3, Sora's room-to-room movement was a lot of fun to use, but the larger scale movement option was just aiming at a warp point and instantly airstepping to it-- not exactly a robust or interesting movement mechanic. There are other massive games that make the act of getting around a lot of fun, like Spider-Man, GTA, and BOTW, but I just don't feel like it's in the KH team's wheelhouse to do something like that.
And, if San Fransokyo is anything to go by, with a large world comes incredibly helter-skelter enemy placement. When there are dozens of possible roads between Objective A and Objective B, it becomes impossible to place well-balanced enemy encounters along all of them, and can instead turn into an enemy spamfest with Heartless that snipe you, or, alternatively, appear without any option of keeping up with you.
I think Olympus and Toy Box are the perfect types of worlds-- Grand adventure from the beginning to the end, or a large area that keeps you looping around a few times in different sub-areas. Giant worlds? Too difficult to develop AND make meaningful.