I really wanted Terra, Ven or Aqua, or all of them, to show up in the trailer. Especially Terra. For a minute I thought it was going to be him under the hood.
And I sort of hope it isn't Data Riku. That means an overly complicated explanation and loophole for data versions coming back.
Though I have a feeling it is him....
It might have a deeper meaning though that none of the three were shown. The short appearance of Vanitas though indicates more than just a fleeting involvement of the BBS-cast, also when considering Terra's close ties to both Xehanort and Riku as well as Ven's deep connection with Sora.
Data-Riku is a being that was created by Jiminy's journal, if that second Riku is him I am pretty interested for the explanation of that.