I would like to discuss how fiat money can be more transportable without trusting a custodian. How can you transfer large amounts accross borders in the same was as bitcoins? (I.e. without involving trusted third parties.)

Imagine you live in country A and then move to country B. You can leave some local currency in country A in the hands of your friend and tell him to pay for your future expenses in country A. He will be your trusted custodian!

Let's improve the example to eliminate trust. Now you give the guy your local currency and he gives you BTC of the same value. It's not a trade, but mutual custody. You store BTC of the guy and he stores your local currency. When you need to pay for something in country A, you send him BTC and he pays. This way you spend your own fiat, the one you gave him before. You can also accept money from anybody in country A via him.

Since BTC price changes, from time to time you need to change the amount of BTC you borrow from the second guy, so that you owe him the same value he ows you.