Fedcoin would replace the dollar. If it actually is rolled out it would end the dollar and probably all other digital currencies. This is the way the United States will end it's debt. Other countries will do it as well.
You are mixing up numerous concepts here. Let me explain.
In the future, almost all currencies of countries will be digital. Indeed most largely are already.
Soon we will see some countries go entirely digital with their currencies (ie paperless). The USD going 100% digital will not result in other countries not still have their own digital currencies, just as the US having a paper currency didn't stop other countries have their own paper currencies in the days before computers.
Second, you can't just "end debt" by making a currency digital. The US's debt will remain, regardless of whether its currency is digital or not.
You may be confusing the concept of a digital currency, with a block chain currency (which is what BTC is). A US blockchain currency (aka a smart-coin) is possible in the future (indeed its likely), but what it will not have is the freedom and anonymity that BTC provides (indeed quite the opposite, it will have trackability associated with a person's unique ID details and limitations on usage dependent on the user's ID details (eg age, criminal record, substance abuse, welfare beneficiary, bad debtor, outstanding fines or taxes, etc), nor the global usage that BTC has, nor the mathematical limit on supply. So, as I explained, a so called Fed-Coin, will be hugely positive for BTC. It is the creation of such coins (and the associated loss of freedom that "paper money" and "dumb digital money" provides), that many BTC investors are hoping for as a future huge driver of surge in value as wealth moved into Bitcoin as a hedge and protection.
