Japan might want to consider it soon too.

Why?

Because the country will die soon (in civilization time scale)?

With that argument the world will die soon, migration is just a temporary measure in civilization time scale. So better fix it now than push it to the next generation.

Eh, this seems dubious. If there's something structural within a nation that is leading to lower birth rates, importing excess humans from other countries doesn't actually address the root problem.

Japan already is. Going to Japan today you’ll see that it’s an extremely multicultural country loaded with tourists and immigrants.

Magically, immigration is the _one_ supply shock that has zero impact on wages. Or, the _one_ demand shock that has zero impact on housing prices. The only impact it apparently does have is to make the GDP number go up.

Anything sounds wonderful if you ignore the problems.