With fiat currencies, money is basically an IOU from the central bank. So it is easy for them to give loans by "printing money", since a loan from the central b

With fiat currencies, money is basically an IOU from the central bank. So it is easy for them to give loans by "printing money", since a loan from the central bank is just as good as cash. You could still layer a system like that on top of Bitcoin. However, you might have trouble getting people to accept your bitcoin IOUs as equivalent to real coins. That said, why would you want that? Why not just use fiat currencies where they are appropriate, and leave Bitcoin for the use cases in which it's appropriate? It doesn't need to replace the whole economy to be useful as a technology.