They use use more credit and debit cards, online banking and mobile money, In a few years, developing countries will follow suit. We are a long way from block-chain dominated currencies, but I see it happening. Paper money will disappear, but it is still king for now.
Yup now almost all country govt are telling their country people to use only digital transaction. Becasue to avoid black money storage. We can make black money only wth the fiat currency if it is not there means we don't have other options we must use online or credit or debit cards. So if it happens in all country then automatically the bitcoin will become more popular in all over the world.