the announcement states the warband bank is going to essentially be an account wide guild vault, 5 tabs of 98 slots, and the normal bank is being converted to a tabbed vault as well (unsure how theyre setting the slot limit on those).
the vault API is, to put it generously, practically non-existent. it was designed to minimise the amount of data required to be retrieved/sent so theres less stress on the servers.
we cant request a different tabs data, only the active tabs data is ever returned by the server, so we can only listen for the data from the tab the user clicked on.
we could potentially cycle through them all, actually shift the ui tab (so long as they dont go and protect that), wait for its data to be sent, move on to the next tab, etc, etc, but just like currency/rep/pet list scanning used to do, that interrupts the user in a very annoying way that they wont put up with.
we can hope they add an API function to request data for another tab, and that the tabs id is part of the returned data (so you can request all of them immediately and then processes the results out of band when eventually delivered), but the blizzard vault UI doesnt need that capability in any way, and it would have to be coded to specifically ignore non current tab data coming in, so theres absolutely no incentive for them to add it.
i know theres stuff all i can do about it, its just annoying theyre going in the vault direction.