I think it will be like fiat money, because still controlled by government. And like current fiat money, its depending on their economic strenght. I think it can not called cryptocurrency because central banks still control the supply and the value
Absolutely true, it will be like fiat money, but in digitized form. They will be controlled by the government and their value will be determined by worldwide actions and economy. It will be based on blockchain technology probably using cryptography, so we may call it cryptocurrency.
They will have both pros and cons if this happens. This will kind of promote usage of the other coins as they will not be regulated and will be without restrictions, and also it may create problem to the orthodox people and there will be many such pros and cons.
It is quite far-fetched thought, no surety if this is going to happen, if yes, when.
Concerning the OP statement. I believe if the government national cryptocurrency the currency will be expensive/grow base on there global trading status (1 USD, 2 EUR, 3 YEN, 4 GBP) etc.