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...
We might consider Bitcoin as a legal tender in the future but I'm in doubt about thinking and considering it as the main currency. I'm certainly out of this. But what I'm expecting to happen in the future is that Bitcoin will remain the most profitable investment rather than being used as a currency to make purchases. As people will see being fit as an investment, they will keep doing this forever.
But talking about the value of BTC, it was unpredictable. It changes very often and even IF given the chance to be considered as THE MAIN Currency, I think it was very expensive than of today.