I really don’t see the issue with this, the idea is to get money from the people you share with. Therefore the actual subscriber pays no more, so what is the issue?
If you share with people who live with you that’s allowed, if they don’t why would you pay extra to share your paid subscription. Yes it was nice to share, but it doesn’t benefit you, the subscriber. It was just a bonus for your freeloading friends (joke).
Implementation would be the hard bit, my kids are all living at home, they have phones and iPads, we also use when abroad on holiday. Therefore they’d have to look at patterns of usage. Plus other examples given when kids in a colleage dorm, unless the current T&C’s define that as a separate home.