The moment all the countries convert to crytocurrency would be the beginning of many amazing things to happen to the world and the financial sector, the process sending and receiving funds worldwide would become very fast and easy, it would lead to growth of businesses and make life easier for citizens of the world.
that would be really amazing if could happen.but i think it just our imagination and could not happen in near future.moreover many government still confuse with bitcon regulation.
There will be more chance that government will not be pleased by how the bitcoin protocol works. In a sense that if a government will adopt to cryptocurrency, they will need to utilize their own customized cryptocurrency for the sake of their own custom protocol since not all government have the same systems. In addition, the most possible crypto conversion will be stable coins.