"The next scene shows Riku and Mickey in an area that is almost definitely the Realm of Darkness before they meet Aqua. Although their conversation about being stronger doesn’t really reveal much, the fact that Riku’s hair is different from how we’ve previously seen it makes it seem as if this is before he returns from the realm of darkness and presumably gets a haircut. Although nothing is set in stone, it’s getting a bit easier to piece together certain aspects of Kingdom Hearts III’s story."
Chances are this is when they first arrive in the Realm of Darkness and this is Mickey commenting on Riku's tendency to doubt himself. It's clear they haven't found Aqua yet so it's definitely one of the earlier scenes. Plus when Riku's keyblade is broken, he has his new haircut so maybe it gets burned off by Aqua or something causes it to become shorter. "A very interesting scene comes from a conversation between Sora and Larxene in the Frozen world, who reveals that Organisation XIII have already found all of their vessels. Whether or not this is a lie is up to the player’s interpretation, but Sora, Donald and Goofy’s reactions seem to imply that it is true. It’s also interesting to note that the world behind them is frozen (heh) in time, although why this is happening isn’t clear."
Master Xehanort, Xemnas, Ansem, Young Xehanort, Braig, Luxord, Larxene, Marluxia, Isa, Vanitas, Demyx, Terra, data-Riku (the blocks stacked on each other on the chess board aren't the same as the dice we've seen in the past on a chess piece). I think they very much have their 13 or they're close to it. "Xemnas and Xigbar are then seen having a conversation in Twilight Town about one of the vessels following their path and how they’ll destroy them if they don’t follow it."
That is definitely Ansem, the Seeker of Darkness/Xehanort's heartless and I have no idea why everyone keeps calling him Xemnas when he's definitely not. "Presumably continuing on from a scene earlier in the extended trailer, we also see Vanitas seemingly about to take out Aqua for good. The scene takes place in Land of Departure, in the same room where Ventus is laid to rest, which means the possibilities here are pretty open. Vanitas could be about to split Aqua into light and dark, turn her into a vessel, or even use her to try and awaken Ventus. Vanitas is in the exact same pose he was in when he tried to kill Aqua in Birth by Sleep, which could be purposeful as he tries to draw Ventus out of his sleep." There's no need for Xehanort to split Aqua into light and darkness since it would be giving the light side an advantage. He wants the 13 vs 7 confrontation, not for the 7 to win. They don't even need to add that many additional vessels. It's interesting to note the barrier that's in front of Vanitas when he's about to do that.