I wonder what the failure mode for something like this is (e.g. in bad weather, after a power cut, a car catches fire, etc). Nobody in the country with keys, cars parked so close together you probably couldn't get in anyway... could be interesting!
That's a solved problem, drench the car in copious amounts of water and flush all oxygen with high pressure CO2 tanks.
Indeed, and the usual solution that firefighters choose is to dump copious amounts of water onto the burning vehicle and then drown the carcass into even more water. The biggest issue is that it takes time for the firefighters to arrive - about 10 minutes in Germany by law - and so a fire has quite the time to progress.
You're right though, if every car is a BEV of unknown battery health left for a week+ packed bumper to bumper in a baking hot car park in the middle of summer, that would definitely be considerably worse