Vaan Officially Announced
Yup, there you go. His EX-Burst is Mist Knack, his Alt costume is based off his concept art, and there seems to be our first look at Terra's 3rd form in-game in the screenshots. Hopefully a bigger/clearer scan will appear soon.
ETA: Did make out that his fighting style is based on rapidly changing weapons, so he'll probably play similiar to Firion and Bartz.