BTC was created with a new transaction system without a central authority. The BTC can be used in the future as the main currency that we gonna pay with. But what's gonna be the value of a main currency? What's the value of dollars or eur?
-Answer is: The dollar IS the value. The dollar doesn't cost anything. The dollar is the value.
If BTC is gonna be used in future, it not gonna cost anything, because the BTC is gonna be the value. It not gonna be like Bitcoin cost 50,000dollars... Bitcoin not gonna cost anything because Bitcoin IS the value. But that's probably not gonna happen. We not gonna pay with BTC but with stable coins like USDT...
Well, I don't think any cryptocurrency is going to be the main currency of the day in the future apart from what you just explained, we should understand that no Government can be the owner of Bitcoin and since the strength of a Nation is a factor of the strength or Value currency of her currency and this cannot be claimed in terms of Bitcoin by any Government, it is rearly that they will make Bitcoin their main currency. People and Investment can accept Bitcoin and other cryptos as it is now but that don't mean it will be the case across.