Re: KH2 Ending Discussion Thread ***Major Spoilers***
I think KH3 will be about the origins of the keyblade. Of the three keyblades in the middle of the feild, we know two of them for sure as the Kingdom Key and Mickey's Keyblade.
The third keyblade, as some of you may already have noticed, has the heartless symbol at the end of the chain. I think the scene is about when the keyblades were discovered. One story of the keyblade master said he destroyed the world. The other story says he saved it. Then there's the story Kairi's grandmother told about the light and it being shattered. I believe that all the worlds were once one whole Earth.
I think that after the finding of the keyblades, the knight who took the "Heartless" keyblade went corrupt, created the heartless, and destroyed the world, thus the Keyblade Master that destroyed the world. But as the story goes, children (possibly the original owners of those hundreds of different keyblades) recreated the world in seperated fragments. With the threat of the heartless still existing, the knight who took the Kingdom Key sacrificed himself too create the walls that seperated the worlds, preventing the heartless from reaching and destroying them, until the time came that someone who was worthy of weilding the Kingdom Key (aka Sora) came to exist, thus the story of the Keyblade Master who saved the world. What became of the third Keyblade Master? I can't really figure much but that they possibly contained the heartless to the world of death, explaining why Mickey had to go there to get his keyblade. I have absolutely no ideas as to who the forth person is.
That is my theory on the end video of KH2. I worked really hard on this, but I think it was worth it.