That is a valid vision when people are trapped in their countries decades ago. People are unable to travel in search of greener pastures! The ability to travel is a game changer and finding jobs away from your area helps workers.
That is why companies now understand workers and not trying to hold on to workers who intend to go out of their employ. It helps the workers personally, and maybe, just maybe, the company can replace them with workers from afar that are better than the ones who left.
Once there will be lesser travel restrictions, and the only thing that matters is the ability of persons to pay the indicated fare, we will see people of different nationalities working in different countries. Such is the effect of globalization --> superior organizations manned by competent international workers, able to produce more goods and services in a more efficient manner!
The question is when. Nations still go to war because of boundaries, beliefs, etc. That thing will start when people have no more implicit biases, on national boundaries and protectionist rules!
we are now about Japan's population, but they are a rich country where is more work for its people. we are poor a country with a huge population, a declining birth rate is better for us since there is not enough jobs to go around for our people.