But even right now or even before, we still can use our BTC as a main currency as long as we are on a country that allows it and even if not, we still can do bypasses and shop directly online using it.
So far, only a handful of countries have accepted and allowed the use of bitcoin as a currency or means of payment. Not many countries do so and i don't think governments will legalize bitcoin as a currency anytime soon because it doesn't benefit them and most countries have their own currencies.
As for using bitcoin illegally, I don't think it's a wise idea. If you don't need government legitimacy you can also use shitcoin or any asset as currency as long as you reach an agreement between seller and buyer, not just bitcoin.