Obviously, with this being a title as major as kingdom hearts 3, there's going to be a fair addition of new worlds. Although there are a couple i'd like to see return in the game. 1. Port Royal This had one of my favorite fights in the game, being the grim reaper, and there's quite a bit of potential for another run with this world. If it focuses on Dead Man's Chest/at world's end, you could feature Davy Jones as the main antagonist of the world, which would make for a splendid boss fight. In addition, the whole prospect of his heart in a chest would fit well with the world, possibly bringing up the question as to whether or not he's a nobody. 2. A variety of final fantasy worlds (Such as Cocoon/Pluse and Midgar) These types of worlds have a lot of potential to appeal to those who would like a more serious plotline. It would also be able to tie up some things left as possible cliffhangers in previous games, like Cloud vs Sephiroth, and Zack disappearing during the ending credits of BBS. 3. Atlantis (atlantis: the lost colony) This was one of my favorite movies as a child, and i would love to see it featured as a world. A leviathan miniboss would be nice. 4. The Realm of Darkness This was playable in the final mix version of birth by sleep, if i recall correctly. But it's supposed to be an entire realm, not merely a single world. So i would say that they should make it either an extremely long dungeon, close to the end of the game, or have worlds of it's own featured in here.