Your title and post content don't match. In the title, you mentioned BTC as a means of payment (as a legal tender within the country), but in the content, you talk about BTC as a central reserve for every country. While the latter is bound to happen, I am a little skeptical about BTC as a means of payment for masses. Bitcoin will be considered an asset class like gold and silver based on the massive holdings of whales and the amount of total BTC in existence.