In many other circumstances it would certainly be an unwelcome precedent, but, this probably isn't as nefarious a hidden kill-switch as you seem to be implying.

In many other circumstances it would certainly be an unwelcome precedent, but, this probably isn't as nefarious a hidden kill-switch as you seem to be implying. The vendors already have and regularly use the capability to push remote software updates, including to low level components like the bootloader or radio baseband. An update to the bootloader which turns it into a display stating "this device is an explosion risk, return it for replacement immediately" and shuts the phone down wouldn't be far-fetched.