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...
Not sure what you mean here. First of all, what does "main currency" mean? Bitcoin is a currency. Primary or secondary, doesn't matter. Bitcoin won't be replacing fiat anytime soon. Both fiat and bitcoin (including other crypto currencies) will be used along side with fiat currency. Are you trying to say that 1 bitcoin = 1 bitcoin? Yeah, this is what we want, but right now that is impossible. The market is very volatile and for our convenience we have to measure the value using fiat or stable currencies. Maybe in the future a cup of coffee will cost half a satoshi, but for now its going to cost around $2.