Declining/Aging Population becomes the issue. Solutions will probably come from Biology/Nature.
Human Quality of life seems to flip the natural "evolutionary script" wrt to population growth. Shrinking population = shrinking landlords/bankers/labor/traders/military/scientists etc
In nature, where there is environmental instability/resource scarcity you see a Quantity over Quality reproductive survival strategy (which is similar to what we see poorer regions of the world) that fuels population growth.
On the flip side, where there is resource abundance and stability there is growth in population. But we don't see that happening in the richer/higher developed regions with humans.
Its like advanced human society/culture has worked out how to override biology.
We currently work around falling population(and the shrinking factors of production) with tech/automation, financial/military arm twisting and immigration which gives rise its own social and cultural instability.
Nature has found other population models though. Ants(Eusocial insects) have solved their population/survival issues by have a single Baby factory. There are theories that the Haplodiploidy it produces makes ant societies function smoother. While Meerkats have collective breeding model which is similar to what certain Feminists talk about when they say Make Kin not Babies.
It will take a couple generations of futzing about in unnecessary directions before we solve these issues. So patience with the people who don't know what they are doing is key.