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...
Foremost, bitcoin being the main currency is close to impossible because the government won't allow it to happen in the first place. The central organizations wouldn't permit the blossoming of bitcoin and before it even start to soar, they would definitely stop it instantly. But if it were to be the main currency, I bet the price of it would depend on the supply and demand because in the first place that's what really distinguishes the price position of bitcoin. The market demand and supply circulation as well as the season would predict what value it may hold.