There’s another thread where inventories are under discussion that might be relevant; it’s more about lacking inventory space. ("Inventory is full!" - Inventory Space) I also bring up the idea of account/realm-wide banking there, so already I’m a fan.
But, I am not that into the idea of having access to this inventory anywhere, whenever, because it would then be used by a lot of players as an extra bag that you can just dump all the BoE/BoA items into in order to counter the limited inventory space made up by your bags. It should rather act as another type of bank.
That being said, access to these banks should probably be more accessible than most banks, as they largely replace the need to use mailboxes - which are everywhere. Perhaps you could literally access it through mailboxes, that would be a great solution that negates the need to create a new NPC or other item to interact with.