Also, just to clear up a few points of confusion:
Void Storage vaults will be per character, not per account. We're still very interested in providing a way for players to share BoA items cross-realm, but there are a number of technological milestones we need to reach before we can make that kind of service available.
The prices for unlocking a Void Storage vault, depositing items, and withdrawing items are still under discussion. The values shown in the blog screenshots should not be considered final.
You don't need to place an item in Void Storage in order to use it for Transmogrification. The systems are completely separate. They're designed to complement one another, but not require each other.
Most tabards will be eligible for Void Storage (excluding a few which cannot become soulbound to a character).