1. Countries that have an economic embargo so that they cannot access certain currencies in trade transactions.
2. Companies/entrepreneurs who have strong political opponents. Political opponents in power try to block access to international and domestic trade transactions. So companies/entrepreneurs use Bitcoin as an alternative transaction tool.
Then, the question is whether Bitcoin can become a world currency one day.
In my opinion, this is influenced by the law of Action-Reaction. The bigger the Action, the bigger the Reaction. The greater the action of political pressure, economic sanctions/embargoes, including geopolitical wars against certain countries, the greater the global reaction to using Bitcoin of its kind as currency. The greater the threat of global rulers to the freedom (freedom) of companies/owners of capital, the more fearful they are of trying to defend "life" with Bitcoin. Besides, the price of Bitcoin is very expensive, poor people can't buy it and I also don't think Bitcoin can balance the poor and the rich.
It's very unlikely governments will allow Bitcoin to become's the world's next reserve currency. While it holds promise to make money better by eliminating the middleman, it won't solve the gap between poor and rich people. Market prices are irrelevant here, especially when people can just buy fractions of a BTC (satoshis) without "breaking the bank". The problem would be getting poor people to use Bitcoin as they lack Internet access, or even a device (phone, tablet, or PC) that would connect them to the Blockchain.
I don't see the world getting better when Fiat currencies are the dominant force of the economy. At least, we have a choice. As long as Bitcoin remains decentralized, there should be nothing to worry about. Just my thoughts