The rational part is that one day the parents may get into conflict and instead of playing cooperatively they will start playing against each other. At that moment the one which focused last years on their professional skills will have an advantage against the one which focused on child care. Dividing the household and child care is the most simple (and most likely suboptimal) way to reduce this advantage.

Indeed this has been the case. I have had such an advantage during our crisis and that is one reason I could deal with it. But then caring for four children is also something you can specialize in and also has a high worth in most countries and is also some kind of advantage.

Somewhere between an extended family and a kindergarten; like a small private kindergarten where the parents are close friends with the caretakers.

Sounds like a kibbuz. I like this idea. But I still think that a professionalization of 'motherhood' wouldn't be a bad idea either. It has the advantage of high motivation. I once even read that this is generally an overdue and possibly needed step. Just cam't find the ref.