Hello, as the title of this post says, I have thought of a possible theory about how modern characters (time line wise), such as organization members, could possibly be the black hooded people seen in the back cover trailer.
The way that this might be possible is hidden withing one segment in Kingdom Hearts X and UX and one cutscene in the same game.
So as most people know, during the first anniversary and second anniversary events for Kingdom Hearts X, there were special anniversary missions for the first, and event for the second. The reason why this is important? Simple, Goofy, Donald, Chip, Dale and most importantly, Mickey all appear in the event. The first event is even suggested to appear as cannon since it appears as part of the main story in KHUX, with the gummi heartless in a large portion of mission following it.
(Note: Possible Kingdom Hearts X spoilers below.)
The one other thing that connects to why I believe it is possible for modern characters to play a part in Unchained X is one cutscene about Chirithy. At the end of this scene: https://youtu.be/oSQBdJayaXI?t=3m29s we see that Chirithy's are actually dream eaters. The reason why I bring this up is for one of may possibilities. What I belive a possibility of how the world of Daybreak town can be accessed by modern characters. I believe it is possible that Daybreak town is a sleeping world, which would explain why Mickey is able to come to Daybreak town despite the fact that he would not be alive at the time of The X blade war.
Thank you for reading this theory, but before I go, here are just a few holes/other possibilities that I thought of while creating this.
1.Despite the fact that Mickey and friends are in Daybreak town, it is possible that this version was created by the book of prophices, which a power suggested the book has by malifecent in the Re;COm movie
2.Chirithy is a dream eater, but we have seen a case of dream eaters in the real world with Riku and his dream eater being in the real version of The World That Never was
3.Tetsuya Nomura confirmed that KHX takes place before the X-Blade war. This could mean that either the world is not a sleeping world, and the Mickey that appears is real or fake, or the events in KHX still are in the same spot, but can still take place in one of the retelling that sleeping worlds preform, but the real events of KHX happened long ago.
4.Traveling to sleeping worlds that were consumed by the darkness a before the events of KH1 has never been shown, and is possible you need to be in the body of that time period, as shown by Sora and Riku being in their KH1 bodies during DDD, around when those worlds were swallowed by darkness.
That is about all that I can think of, despite the possible holes that I bring up, I believe that this is a possibility, one of many.