part you might not know about: the economic impact of the one child policy.
The population shrinkage can be remedied by encouraging more migration to China. That has been happening already and currently at least 20 percent of the population is foreign born.
Usually they know things behind the scene, but I'm not sure where they got that 20 percent number.
Wikipedia says there are only 30 thousand OFW in China, but a lot more if you include Macau (15000) and Hong Kong (200 thousand).
We have relatives working as nurses in Macau.
But a lot are from North Korea, or from SEAsia, especially VietNam.
China welcomes skilled workers, but the dirty little secret is that locals have better opportunities, so factories hire outsiders, often illegal immigrants, or those who come in on a "visitor visa", get a job and overstay their visa, or those who come on "visitor visa" and go home and then return again (legally) on a visitor visa so they can continue working.
Foreigners, doing the jobs locals don't want to do.
Wikipedia even has a page about this. More HERE.
Immigration is pretty widespread, from Nepal sending workers to India to Africa sending maids to Saudi to China bringing their own workers to run businesses in Africa, to Korea sending people to the Philippines to learn English and who end up staying.
And we have relatives in the US, Canada, Italy, Germany, the UK, and Macau, and who in the past worked in Kuwait and Saudi.
The Philippines has lots of foreigners living here, mostly retirees but also those who marry locals and start businesses (foreigners can't own land or businesses, but extended families can... and this tradition goes back a couple hundred years, which is why most elite families have Chinese or Spanish ancestors).
And note: One Millianon OFW in Saudi,
Saudi Arabia's population as of the April 2010 census was 27,136,977: 18,707,576 Saudi nationals and 8,429,401 non-nationals.
If war breaks out in Saudi Arabia, the problem will not be loss of oil (the US is now energy independent, thanks to fracking) but the huge exodus of millions of people to poor countries.
India made a film about their evacuation of their 170 thousand workers from Kuwait after Saddam invaded that country in 1990.
If the war in Yemen spreads, it will be a really big mess for us.