Terra is the next in the set to be revealed. They didn't have the prototype ready when Aqua and Ven were shown off.
Xion's Bring Arts figure is releasing in August.
The more you know.
Speaking of it WTF is wrong with the Square Enix EU store. They allow me to place a pre-order for Ventus, Roxas and Xion KH III Bring Arts, but not Aqua?
On Riku's figure they have an "sold out" moniker but Aqua isn't even in the store, only the 0.2 Play Arts Kai version.
Oh and btw why is Xion's figure a whopping 15 Euros cheaper than Ven?