Just imagine if the Federal Reserve started their own cryptocurrency, created a FedChain, blessed the banks to use it, ect. I can't imagine the limitations on it, but I am sure they would be bad. Probably would be a way for the feds to create their own coins in the protocol.
Soon there would online exchanges like Cryptsy.com that would allow you to quickly switch your FedCoins to BitCoins.
I think ultimately, this would actually accelerate the fall of the dollar.
This is why the Federal Reserve will never create a Fedcoin. It would make the escape from fiat much easier.