As an optional paired peripheral, it's a good idea, and perhaps we will look into it further if the main product has some success. If individuals consider it a valuable addition then they could pay to have it installed. A secondary drawback would be reduced battery life on the device, as it would be continuously paired over Bluetooth whenever the stove is in use - usually it is just passively advertising in case you are trying to connect through the phone app.
In terms of saving lives, the automatic cut-off would make a relatively small difference - fire department stats (on smoke alarms) show that having a loud beeping alarm is extremely effective at attracting attention and is enough for the user to go and turn it off manually, or to get out of harm's way if things have turned bad. Where the automatic cut-off would help is in reducing the chance of the house being damaged by smoke or fire when the user is out of range.