Personally my thinking is that there's no more ammo left (rates @ zero already). That plus Yellen seems to care too much about how much others like her (remembering some news blurb I can't find now about her promising to really raise rates next time). Then again, if China's dumping raises rates...
At this point, I see as the real concern is that China, or anyone - including the US or other private sector, isn’t buying our bonds then we (the FED) has to buy them from ourselves?
Redeeming some holder’s short bonds and then buying our own long bonds...this just another form of kicking the can to delay the inevitable.
If it wasn’t government doing it, I think it would be illegal - or should be. Sort of like the analogy of borrowing on one credit card to pay what is due on other CCs. And we know how that always works out.