It is absolutely unrealistic that bitcoin should ever replace all currencies in the world fiat. With such high volatility of bitcoin, when he now jumps in price for thousands of dollars every day, then down and up, and if he grows up in price, then, accordingly, his price will change by tens of thousands daily, no state can plan development of its economy. In addition, many states were treated earlier and now continue to be hostile to each other and will not want to use one currency and depend on each other. Wars have already occurred since the birth of our civilization and are unlikely when they will cease. Therefore, until then and the chances of bitcoin, no one will become a single currency in the world, even under the most favorable conditions for this.
fiat is a form of special economic sovereignty, to the extent that they will not accept bitcoin as a second currency, but the prospect will be different if America ends up wanting to consider bitcoin as a common currency all over the world, many countries will appreciate and tighten rules positively. But bitcoin will remain in a position not as the successor of fiat, just a common currency option.
