For being in the 21st century, I'd say paper money should be phased out as soon as possible. Everything should turn digital, as we live in a digital society.
This can't really work in some countries typically in Nigeria. This is what has being causing comotion in the country for days now as there is a big scarcity of Naira note. Even a protest was made in Ibadan, a town in Oyo state, Nigeria base on this scarcity of this naira note.
https://www.thecable.ng/roadblocks-bonfires-as-ibadan-residents-protest-fuel-currency-scarcity/ampDigital payment can't really work for some countries because of
1. Bad network
2. High price of data
3. Illiterate old people.
I love digital currency but I don't see it in use in Nigeria soon.