Instead what will happen is that they will probably have a 10 times more efficient system of vetting the highest quality migrants from around the world than even the US, utilizing their future hyperpower advantage.
So, at that point, there is no reason why an immigrant couldn't be from Brazil, Nigeria, Europe, or whatever, but has to be from some neighboring countries as you said, since everyone can basically buy a plane ticket.
Cultural assimilation is also not a problem, as the highest quality, high IQ migrants are generally not so dogmatic, it's mostly lower level ones that are hard to assimilate.
ffs dude be realistic. you talked like one of those single middle aged women who want to get married but say they will not settle for any one shorter than 6 feet and making less than 6 figures annualy.
what percentage of people world wide fall in to this category of "highest quality, high IQ migrant"? say may be at best the top 1% or probably less. in the year 2100 1% out of say 6 or 7 billion people is 60-70 million. in the year 2100 the total world population will actually be 10 billion however more than 4 billion of them would be Africans that is why I excluded them. after all I'm sure China wouldn't want to be a nation of dozens of millions or even a hundred million Africans.
so out of those 60 million "high quality IQ" people how many would chose to stay in their home countries and how many would chose to go to the west or other neighbouring countries and how many would chose to go to China? especially considering that Chinese language is the most difficult language to learn? at best may be 10 million would go to China? 10 million people would be a drop in the bucket for a nation like China. pretty useless.
if we are talking about attracting scientists like the Einsteins of the world & that's what you mean with "highest quality IQ" then I'm pretty sure China, the US and many other countries already do that with cash incentives.
I don't think the demographic issue in China can be solved with immigration, however if immigration were to be the solution then it cannot be this unrealistic nitpicky kind of immigration. instead the only criteria should be:
"#1 are you from ASEAN (excluding Indonesia) or Nepal or north east India?"
"#2 do you have a criminal record or not?"
"#3 do you speak any of the Chinese languages?"
"#4 can you take care of yourself financialy?"
"#5 are you commited to integrating yourself into Chinese society?"
"if you satisfy all the above criteria then here is your Chinese citizenship"
for production you have automation, for consumption you have belt and road. so there are probably ways to progress that are more aligned with socialist ideals.
land without people is useless. because population is what brings life to the land and develop it & build it up. when countries are at roughly the same degree of development population size is what determines a country's strength and place in the world. why else do you think China is much stronger as a nation than say South Korea? that is because China simply has a far much larger population.
if you think in the future automation and exports will mean population size will become meaningless then I guess that means in the future a small country like South Korea can just buy/produce a fkton of robots and then become as capable as China.
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China is far too big for it's demographic issue to be solved with any kind of immigration. the only solution is for Chinese women to have more babies. there is no other way around it. the government has to make life easier for people if they get married and have kids with incentives and at the same time make life harder for those who refuse to marry and have kids through taxes or other means. just as how China was able to force people to have less kids. they should also force people to have more kids now.
low fertility is not only a China issue. all advanced nations are facing the same issue. as for why it's happening.. well some people say it's because of feminisim, that is the modern woman just wants to work and not have kids.
personaly I don't believe that is entirely true. almost every woman I speek to regardless of financial or education level wants to have kids. you can almost see their maternal instincts in their eyes. they all deep down want to become pregnant. and for the older women.. I have never seen a childless older woman who isn't sad and regretfull. wanting to have kids is in the DNA of women.
I believe these are the reasons why the fertility rate is low:
1-women are programmed in their DNA to seek men who are better than them. however since women are getting richer and richer it is getting more difficult for the average man to impress a successful woman. for some women once they achieve financial independence in life she thinks she is the sh*t. at which point she will refuse to settle for anyone who isn't tall as fk and richer than her but then she fails to secure that top 1%er because that top guy has ten other women chasing after him and is in no hurry to get married because there is no biological clock for men. and by the time she realizes she needs to settle for some one on her level she is already at an age where pregnancy becomes difficult.
2- the requirements for a happy life in the modern world are far greater than for the older generations. people want to have enough money to buy all the electronics they want. and they want to have enough money to travel and see the world etc.. getting a house nowadays is much more difficult than what it used to be. all this forces people to delay marriage or outright drop the idea of marriage and kids because they need more time to build themselves up.
some people say as societies become more prosperous they are less likely to have kids. personaly I think that is only partialy true. I think a better way to say it is when societies have higher aspirations they become less likely to want to have kids because they need more time to achieve their goals and at the end some of those people who abandon the idea of family fail to even achieve the kind of massive financial success that they dreamed of so they get nothing in the end.
after all true prosperity would be.. to be financialy well off and own a house while you are still in your twenties at which point getting married and having kids won't be a financial burden at all and it would just be the cherry on top.