Well, any entrepreneur must ask two questions to succeed: For what is there a demand? And how can I supply it without losing my shirt?
If the demand we set out to satisfy is a credit union that will loan even in such a credit crunch as this, we're in a great position to do it. We promise to keep full reserves, we set up with any nationwide ATM network that will have us, and we run your basic FRN based credit union. It won't be the most convenient bank as we are unlikely to try to set up brick-and-mortar branches in each city, but many of us libertarians will put up with that to be part of the solution and not the problem. Those of us who are forced into the banking world because our employers insist on doing direct deposit will be there with bells on.
We could set up a bullion depository with a twist. Deposit your pms with us and we'll loan it and pay our costs (at least) with the interest. So, a safe, cost free depository for us. That would be useful enough to get deposits. Why leave your pms sitting around and doing nothing? Why even invest in a safe? Of course, the loans would have to be paid back in pms as well, so borrowers would have to convert on both ends, but in a credit crunch surely many would be willing to go to the trouble.
Or, we can shoot the moon and try to combine the two. Since the overwhelming majority of us get paid in FRNs and everyone needs them to pay bills and such, this would involve the institution becoming depository, lender and dealer all at once. The deposits could be made in FRNs, the pms bought, the loans made in FRNs and the interest used to cover expenses and salaries. These would be highest in this scenario as you'd need someone to figure how much to pay in taxes on each transaction if and when the pms went up between that customer's last deposit and this withdrawal. This would be a pain, even with computers, of course. But depositors would be able to make a boast no other bank customer could claim--their account would be inflation-proof. Again, an ATM system would make it possible to do all this with only one brick-and-mortar facility.
So, pick a battle. How far do we want to go and could we break even doing it?