I bet there's some way you could make it work, like maybe you'd cap the amount to be loaned based on how much you own in the bank(i.e. someone with 1000 Neopoints could only borrow up to 500 NP or something). And when you did, the bank would make you pay a tithe every time you made NP on anything--games, auctions, shop sales, stock sales, even wins from the Tombola and Fruit Machine.
Ooh! And if you didn't repay your loan within 6 months or something, they could make you unable to spend any NP until you repaid your debt!

And they'd start charging interest, and reposess your items one at a time, and close down your shop, and sell your Neohome! It'd certainly teach the youngsters about debt...and I'd enjoy it, even though no one else would.