For power to really continue to stay with them, they need to protect the fiat and continue to enforce the physical cash, but no matter how much they continue to hold on tight, one day, the system will automatically adjust right before them, and they see that many people starts to use cryptocurrency even without their full approval or support which will break the power of fiat over their citizens.
Well, actually they are not really protecting Fiat currencies to prevent anonymous transactions, it is more about "control" ...Yes, we know some governments are fixated on civilian surveillance and anonymous transactions is perceived as a threat, but most Cash transactions are anonymous too and that is why some of these governments are looking at technologies that would enable a transparent Cash-less society.
The future of Crypto currencies, would be a world where you have different ways in which people would use Crypto currencies, namely :
1. Regulated "Private" Blockchains - Where KYC/AML regulations are enforced.
2. Unregulated "Public" Blockchains - Where people would bypass regulations and would use direct transfers between two anonymous entities.
3. Formal GovCoins - This might be digitized versions of local Fiat currencies that use Blockchain tech to create centralized ledger systems to track and control all transactions.
We are moving in very strange times, where Blockchain technology can be used against normal citizens to invade their financial privacy and where governments takes control over people's wealth.