Bitcoin already has the capability to be used as a currency. The problem is core developers are holding it back. Especially when it comes to on-chain scalability. There's an off-chain scaling solution called "The Lightning Network", but so far, it's full of bugs. The main issue would be dealing with wild upswings in market price (volatility). After all, people continue to rely on Fiat as a standard unit of account. If goods and/or services were valued in BTC instead of Fiat, things would've been different by now. But I don't see this happening anytime soon. Not as long as Fiat continues to exist.

I'd say Bitcoin becoming the currency of a country is nothing more than impossible. Not even El Salvador was able to do it with success (despite making BTC legal tender). While you can technically use Bitcoin as a currency (medium of exchange) to buy stuff, it's certainly not a practical solution. At this point, it's hard to change BTC's status as a store of value. And I'm afraid it will remain that way forever.