Yes, you are right on the situation that the market volume will increase enormously. But I don't think this will ever happen since the governments are so much related to the banks. And as you may have guessed, banks would be in the deathbed if governments accept the cryptocurrencies.
I can have a forecast of the situation that if governments are accepting cryptocurrencies, it means they are planning to make trades over the borders with cryptocurrencies. Well, not all but in some situations, yes. So, banks would not have enough backup to stand where they are, and their numbers would be decreased increasingly.
We will see what will happen in next 10 years I believe.