I think that imagination is going far beyond than the existing people.A single country could only be able to buy all of the bitcoins only when every one is ready to sell their bitcoins.Not all of the bitcoin holders are like newbies just selling bitcoins without any ideas.We could hope that considerable volume of bitcoin users will be early investors who would like to hold it for more time.So,such an idea really would not work out.
Today the Netherlands said it has 500k+ users in cryptocurrencies and in October it was only 150k still. So it will most likely exceed 1 mil this year. Then look to possible growth from the US. Gonna become crazy this year no way to deny it.