Just to start with, you can check the below link,
https://en.m.wikipedia.org/wiki/Legality_of_bitcoin_by_country_or_territoryIt will give you a fair idea about the legal status if bitcoin worldwide. While few countries have come forward to create detailed regulatory framework for crypto usage, majority of them are still lacking a formal framework. So it is very difficult to say which country will join the bandwagon next!
I personally think a series of African countries will soon join the race of cryptocurrency by making it legal because it will benefit their economy directly and indirectly. Developed countries will take some time here!
I could see that there are many countries now that made the legality of cryptocurrency possible within their borders, compared before. Given the case, however, I still find it hard to even guess which country would be fully adopting cryptocurrency. Aside from it being legal to a country, there many things to consider such as tax, trade system, fees, transaction framework and most of all the willingness and interest of the people to embrace it.