e: over post limit
Equilbirium doesn't have to be current population level. maybe japan with 60m population and lower urban density to enable average house size increase from 1000 sqft to 2000 sqft + other interventions will get TFR closer to replacement @ 60M. Govs still going to have to pile on lots of carrots and sticks on top to make decisions swing towards 2 kid+ households. But it seems like most of Asia/Europe pop density + limited housing is one impediment to raising families.
Sustainable equilibrium is replacement TFR.