Consider this: 1 slot, and once you take something out, you can't put anything back in for 3-7 days. Available for ~200 TP. Still useful for passing the occasional BtA item, but doesn't render the 20 slot unlimited access extravaganza that is the current shared bank useless. Heck, it may even prompt people to upgrade to the full bank once they get a taste.
I know I'd pay that price, while I'm very hesitant to shell out almost 1.5k for the shared bank since it wouldn't see much use.