From many months i am thinking about what if " we remove fiat system , and change things into crypto " .. What are the main difficulties we will face ?

1. Internet every where is not yet done.
2. Awareness with Crypto ( but its not a big thing, as most are aware of how to use currency. )
3. Bitcoin is only 21,000,000 and world population is more. ( This can fix by other altcoins same like USD/RUB/CNY etc )

What other difficulties we can face ?