In the vein of Birth by Sleep Final Mix, we get an addition onto Dream Drop Distance HD: Kairi mode where she finishes the test that Sora and Riku would have done without Xehanort's interference and awakens the last Sleeping World. I don't count Destiny Islands as an actual world. You don't even see the island and it's a boss battle with a character from another world.Yen Sid said:I have come to learn that you, too, can wield a Keyblade. I am glad you are here. Master Xehanort has returned to gather the 13 Darknesses and we must be ready to oppose him with the 7 lights. You, Kairi, are begin training to use the Keyblade with a true master to teach you the proper way. As such, King Mickey will watch over your training as you enter the Realm of Sleep.
As for which world that would be? Daybreak Town. And instead of interference coming from Master Xehanort, it comes from the leader of the sixth faction. You also get to meet Skuld and Epherema, as well as getting to take on the five Foretellers.
We'll also go with eus-mylus's concept of dream eaters as weapons.