The thought came to my mind, when everything about Bitcoin and Ethereum is legit open-source, and posted on GitHub; there's every line of code available in the open for any government to make a Bitcoin/ Ethereum clone of their own. So, whey aren't they doing that, if not seriously, then at least proof-of-concept?
How do you know that they're not doing that already?
At least the countries that plan some sort of digital currency (Sweden, Marshall Islands, Venezuela ...) surely have already downloaded and reviewed the source code of an open source cryptocurrency and it's very likely that they already have modified it to try out a "pegged" version internally. I can also imagine that all big economic powers, from China and the US to Russia, will already have done that, at least to look how it works.
But as stompix said, a centralized cryptocurrency does not really have too many advantages with respect to a "State Paypal" with a client-server model. So I expect most of the "state digital currencies" will follow that model.
And no,
patented cryptocurrencies will never be a replacement for open source coins, as they are necessarily centralized and thus vulnerable to external pressures (e.g. government imprisoning the development team, or more subtle pressures ...).