I'm not sure I would class some of those countries as 'major' ... but there is a general sense now that bitcoins are leaving the USA, and at an accelerating rate.
It is possible, but the existing fiat money are still available anytime I think all of these are not exactly being canceled and replaced it into Bitcoin currency, this is additional currency in whole country in the future.
Bitcoin will always remain an alternative currency. Not all people will use it, because many simply do not trust crypto currency. But I am sure that in the future the crypto currency will be very popular