The Great Firewall of China is designed to censor the flow of information into china. It doesn't work. People deliberately misspell banned terms. If you write "Tiibet independence" everyone knows what you mean. (Yes, I know Chinese doesn't use the Latin alphabet. This is just an example). It is getting harder and harder to restrict the flow of information.
The trouble is, money is just a type of information. When you sign a credit slip or type in your PIN it confirms two pieces of information: your identity and your credit. This is a bigger problem for governments than undermining censorship. If governments can't track money, they lose their tax base.
This is already happening at the edges. Scandinavians often buy their books from Amazon.co.uk, because the VAT rate for books in the UK is zero, compared with more than 20% in Scandinavian countries.
What if governments can't track income, spending, capital gains or inheritance. It is a little hard to hide land online, but land taxes will not support the modern welfare state.
There may come a time when western societies are forced to choose: world government or rolling back government. To restrict the role of government to the pre-New Deal level or accept international taxes? Most people currently regard both these options as unacceptable. But one day they may be forced to choose one of them