I think crypto currency issued by the government and is backed by the government would be calling the same animal a different name. It would still work like a fiat and they could control it but still disguised as decentralized crypto currency. They would either ban any other crypto currency adoption in their country or tax other crypto currencies higher.
Seems a good idea if they create their own currency, but giving the option of using decentralized Crypto-Currencies too to their citizens. The problem is to forbid one kind (the decentralized one) to force everyone to use the one they want (centralized). Indeed a centralized Crypto-Currency created by a government would be very similar to fiat, however they would be using a new technology, what would be already an advantage, an improvement compared to the old system.