"This is about the time that defenders of copyright and trademark will chime in to suggest that intellectual property enforcement has led to the creation of new intellectual property, thus fulfilling its purpose..."
...Which sounds suspiciously like the Broken Window Fallacy.
I use bluetooth headsets, myself. Those won't transmit sound back when they're in streaming mode, and if they're in headset mode, it's a live mic by design. (Also much lower quality sound.)
Except on my desktop when I'm playing video games, and I've got a mic plugged in anyway to talk to my gaming buddies. No need to get elaborate. But what you hear will probably not be terribly interesting unless you're a fan of Payday 2. And probably not then, either.
"There is a simple way to block the attack, keep something playing on your earphones, as an attack would have to check for active use before switching to microphone mode, as silence would make the user investigate their earphones. You do not need to be listening to it, just keep the output mode occupied."
... Or unplug your earphones when they're not in use.
What's new isn't that headphones can be turned into a microphone; it's the combination of that and the fact that the Realtek chipset's headphone output can be turned into an input. I wouldn't have guessed it, myself. (I mean the chipset thing. I also already knew that a dynamic speaker can be used as a mic.)