As far as I can tell...
[spoiler]- Xehanort is trying to get Sora's mentality broken down, either for another shot at the X-Blade (via his and Ventus' hearts), a new vessel (since despite being in 'prime', Terra!Xehanort got his ass kicked twice), or some sort of pawn.
- Sora might encounter, or at least get allusions to, Xion and the BBS trio. The hood with red eyes might be his Heartless and he might finally resolve that (although I could've sworn that was resolved in Coded, but who knows).
- Lea, remembering Roxas and his days as Axel, probably wants to go after Sora and Roxas to save their asses.
- False!Ansem and Xemnas seem to still be around independent of Terra!Xehanort, although that could just be the situation of the dreams (if not, then Replicas are viable). I wouldn't be surprised if Old!Xehanort is somehow separate too, considering the clusterfuck.
- Either there's multiple Mickeys in these dream worlds, or some sort of timetravel [parasitic bomb] is happening. Assuming the former.[/spoiler]
This definitely isn't some sort of simple filler with how much is being hinted at. Sheesh.
With the nod to the first game at the very end there and remembering the secret movie at the end of said first game, I really have to wonder how much of this series they planned ahead of time.