How so? We have two long range Model 3s which have 140+ kWh capacity in total (70kWh/car, conservatively). Even if you'd only allow 50% of that to be used for powering one's house (you don't want to run large batteries all the way down, or charge them to 100%, often, if you care about long-term capacity), each car could provide 35 kWh, or the equivalent capacity of ~3 PowerWalls. The proper electrical interfaces and monitoring needs to be engineered, but there isn't any good reason not to do this. Seems like such a waste. Even if you could only use 20kWh, that's still be a huge win. In states such as Florida (and, now, California) where power outages are frequent, this would be a godsend.

Of course. Drain your car during the outage, get stuck with dead car when it turns out this outage is caused by the fire nearby.