And what is that supposed to help when the thermistor reads environmental temperatures due to having fallen out of the hotend, or due to the heater cartridge having fallen out of the hotend? Or when there isn't an active serial connection to begin with?
Temperature control and monitoring of any kind is the responsibility of the firmware, or better yet, hardware safety measures. A serial client is too far away from the action to be able to reliably intervene if things go down the wrong road.
And honestly, I really don't want to build in half measures that people will then use as an excuse to not flash a safe firmware. Next thing is that this will (predictably) fail in a scenario that could have easily be prevented by existing firmware and people blame me for their laziness with regards to securing their printer. No thanks.