The fed us buying bonds to lower interest rates at rates cheaper than anyone else would pay. That's how they lower the rates.
They are now buying, effectively, about half of all newly issued us debt plus what ever they roll over.
If they unwind their book as you suggest what do you think will happen to bond yields and prices???
They will spike very hard, this will cause all parties including the fed to take huge losses on their bond investments, forcing new selling and a new panic.
It's very hard to see how the fed could unwind its position in the medium term.
