I think Elon's estimates are a bit exaggerated. He expects similar adoption to smartphones. But with a pricetag of 20k USD, it is more likely going to be 1 per household. I've had household helpers when I was younger, and having one for every member of the family was unthinkable. Maybe for the royal family. 1 was enough, and there was a lot of downtime throughout the day, especially when we were at school and work. So if the bot is efficient, there will be even more down times.