I agree it's a great feature, but how many people who would be served by a backup battery don't already have a backup generator for when their power goes out?
I can’t imagine that the backup power from a truck is truly a replacement for a generator. More of a “nice to have because you can” rather than something you’d depend on. If you’re really worried about backup power, you’d have a generator in place.
When I used to live out in the sticks, I lost power at least once a week, maybe more. Usually for less than an hour, but sometimes for half the day. I'd wager over the course of the year I didn't have power for maybe 300-400 hours of it.