I'm telling you, this is not a Kirby stage. Kirby's world doesn't look like this. It's too serious. Look at Smash Bros Melee and the Kirby worlds there. They don't have this look. Let's bring up the disappointment of the disappearing Kirby GameCube game. It seems like it's been moved to the Wii but there has been no evidence supporting this. Anyways, if you go to Nintnedo's site and look under the Gamecube game list and go to Kirby, you'll find a short trailer from E3 '05. Looking at that footage, you'll see that again the artstyle doesn't match up. I've played plenty of Kirby games and unless they've made a drastic change for the new one coming out, I'm ruling this stage out as being a possible Kirby stage. Plus, I think the whole day/night sundial thing adds evidence to this. There is nothing of importance in any Kirby game of such elements. In the vanished GameCube game, the big play element was having four helpers and being able to ride them all. That has nothing to do with this stage.
I'd have thought it might be a Twilight Princess Zelda stage but I guess noght. After all, the Wind Waker had some elements on night/day and I thought that might carry over to Zelda:TP but I guess not. Right now, Raid over the River still looks like the best choice. If you look in the vidoe, this stage is also floating over a river. It just seems the elements are pointing towards that the most.
Actually, the best thing to do would be to take a page from Sherlock Holmes. Rule out, everything that it is not. Then whatever is left is the answer.
I'm guessing since no one posted a guess in this direction it probably isn't a possibility but would this have anything to do with Baton Kaitos? I've never played the game but this picture just struck as something that would fit the stage. Maybe because of the colors. But the artstyle makes it seem like it could fit this stage. Plus it is an island in the sky. What do you think?