It doesn't even need to be the main unit, I'll still be happy, if it's only as a recognized payment alternative, for example. Don't be considered as an enemy to an institution or a party that doesn't like Bitcoin. Globally this would be hard to imagine.
I can only say this is difficult, because so far the adoption is still less than 25% how the world will not allow Bitcoin to be too powerful. There will always be the opposition to thwart it. The absence of a control center is clearly a strong consideration and will be a big obstacle. If we talk about the future, maybe every country will use their own digital currency with a version that is much more crypto-friendly.
It's still difficult, so far adoption has only been carried out in a few countries that have approved Bitcoin from the start.
some other countries or developing countries only provide regulation as a commodity and nothing more. Indeed, not all will accept the existence of bitcoin, such as the government's opposition to bitcoin which does not approve of bitcoin being used in their country.