Like I said earlier, the idea of children being too expensive to raise is already leading to an interesting social experiment where people raise pets in lieu of children. The next step however would reverse feminism especially when children become a luxury. By then, the upper classes are more likely to start and raise families and even practise stricter gender norms.
Not only that, they’ll employ servants be it human or robots so in a sense that aristocracy’s back. When combined with that the upper classes generally have a higher fertility rate than the poorer ones, we’d see families grooming their children to be heirs to their fortunes. If they ever own pets, it’s mostly practical.
When combined with a declining middle class, feudalism and fiefdoms will return as they’ve not been practised for years until now. Even France could return to that stage whilst its ex-colonies like Cameroon and Cote D’Ivoire are achieving social mobility similar to Renaissance Italy and Revolutionary France.