Regarding the title being a spoiler: I think it's safe to say you will be able to lift land from the overworld to create sky islands. Maybe at these points:
If they weren't ready to show that before then people would be able to guess that creating islands is a central mechanic, since the sky islands are tears from the Kingdom below. But then again you could probably put two and two together from the previous trailers already.
Probably also explains why there don't seem to be many changes to the overworld, as time goes on the player will change the overworld by creating the sky islands. Missing land down below could reveal caves, dungeons/mini dungeons, new puzzles, maybe even towns or settlements. And obviously there'll be new areas created by the sky islands.
By the time you reach the end game you could end up with 2 big open worlds: One in the sky and the now all fucked up and torn overworld. And also more linear dungeon areas underground (hopefully with bigger more traditional dungeons too).
It would explain why they're so apprehensive to show too much, because showing the overworld all ripped apart would be considered a late game spoiler.