Fertility really 20/30+ year away problem.

PRC growth now based on educated population, which exploded, not total population. Reality is every tertiary median to upper middle class wage is more productive than 10 undereducated peasants... the ones first to age out. There's like 200-400m+ bluntly useless mouths dragging down productivity/per capital metrics, the only saving grace they did NOT get rich before old, i.e. poor old so it's cheap(ish) in terms of resources (but not labour) to support them. Put it this way, PRC is generating OECD combined in tertiary, disproportionately STEM, they have backlog of 200m births from last 20+ years that still haven't got their masters/phds... at 60% and increasing tertiary we're going 100m+ high end talent, aka the greatest high end human dividend in recorded history who will be in workforce for until 2060s, i.e. so far out its hard to project based on present realities, only they have no shortage of advanced economy growth potential. Like if you throw all projected US newborns + immigration into STEM... PRC would still come out FAR ahead. There is no contest, unless AGI displaces everyone.

TFR real issue probably 30 year out. There will be some rebound, current crashing TFR because so many entering tertiary last few years = delay family formation. Women going to turn 35-40 and realize they want kids... and have them, especially considering 1:4 dependency ratio also = 4:1 wealth transfer + property going other way when previous generation (with high savings rate) dies. But won't get to replacement level. Then it's matter of what bad levers PRC willing to pull - pro natal fertility policies does not incentivize 2.1 TFR... and no one has tried punitive policies, i.e. limit wealth/property transfers to families with 2 kids... all sorts of inducements liberal societies haven't... or politically can't try. Or immigration, test tube babies, who knows. But IMO they try punitive policies first. That's really the only thing that no one has tried, and we know from wealthy Muslim countries with oil money, religious incentive, domestic help... aka every support imaginable, TFR is below 2 or trending towards it.

> finding a solution to something nobody else has managed to solve

In the 21st century, that is definitely something I'd bet on China for being able to do. Across all sorts of problems.

The solution is going to be paying people. No, more than that. No, keep going. Higher. Market-clearing price.

The issue with demographic decline is not just quantity of people, but also quality of people. China (and any country) will want individuals that speak the language, are culturally compatible, with useful skills, and so on. The limited number of people any country can draw on once you consider this starts to make it clear that migration doesn't solve anything.

And even with migration, if those migrants don't themselves end up with high fertility rates then you've done nothing but kick the can, and not especially far. Because of all of these issues, I think there's approximately a 100% chance that China will do the equal but opposite of the one-child-policy should their demographic issues fail to start reversing more naturally.