No, it can't. No way.
It would be totally illegal.
The Federal Reserve, nor any central bank, doesn't have the power to create a new currency. It's duty is to protect, or control, or develop (depending on circumstances) the currency which is legal tender in the country. It cannot create a new currency, and it cannot change the currency it's working with.
It's not really a replacement for the dollar or even a new currency but rather a digital representation of the dollar that is able to leverage the power of the blockchain to allow or trustless, near-instant, and low-cost transactions. The Fed will keep the coin's value stable by readily accepting USD for fedcoins and vice versa.
Replacement or new currency, that doesn't change a thing. The Federal Reserve doesn't have any right or power to do anything with anything else besides the US dollar. the dollar is its one and only mission.