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 ?
One currency economy would lead to nothing but war, destruction and obstruction. One more problem that the crypto economy might face would be the results causes by the end of net neutrality. And to add to your first point, internet is essential but there are not enough resources for people, so care about internet later first, let the being live peacefully. Spreading an awareness to people about crypto would be something that would be impossible to do, everyone has their own understandings, it'd take forever for any economy to embrace crypto as it's main currency. There are tons of issues, we are just not seeing them.
One currency economy should even be the last thing anyone should ever want to think of. This will not work unless it remains decentralized still.
Every country will still have their own currency anyway and just like we have it already globally with USD being placed as the global currency, it can still work without issues, but we cannot really say what the outcome would really be like at the end, but until then if it eventually happens at all.