I don't like the idea of physical cash disappearing. I understand the future is digital payments - but a Bitcoin future means you will need to have a powered device + internet to make payments when you travel. Even 50-100 years from now, there will still be many places on Earth with bad internet coverage/restricted access and losing your phone/having it stolen may mean zero access to commerce.

If we can create a reliable physical layer of cash notes on top of Bitcoin - that could solve this issue.