A premier AP already costs $539.99, I honestly can't see how much more they can push that price up to add a third gate on to the offerings. Bear in mind that this is exactly what they are pitching VB as - a third theme park, not a water park. I don't think they will follow Disney's 'waterpark add-on' model at all.
I predict it will be included with the top AP, which will most likely get a $30 or so inflation increase before June 2017.