My maybe slightly pessimistic view of Japanese attitudes toward immigration is that they will try to keep the Indians in a state of limbo, ready to deport them at the drop of a hat. Which of course won't work at these kind of numbers, anyway.

> I don't know of a single political measure which has significantly raise birth rates.

Economic freedom, and getting rid of pervasive and extreme rent-seeking (especially at the local level) which raises the cost of caring for kids, and for the kids themselves to start a new household when they grow up. You can see this in places as different politically as the Scandinavian countries (e.g. Denmark), and the U.S. "Red" states. It just works, it's simply anathema in every way to all sorts of out-of-touch elites.

This attitude is referred to as "eating your seedcorn" and ... well good luck with that.

>Children are massively expensive, especially to the parents. Parents, especially those who work, can't be "compensated" for the work, costs and risks of raising children. The motivation to raise children is entirely irrational from the perspective of the individual.

So, essentially, no reasonable person would have children. Instead we should have an underclass of people who were, in your words, "irrational" enough to have children to move to another country to work for very low wages and serve and literally change the diapers of the aging, enlightened elite who were rational enough to not have children.

Raising birth rates to a sustainable level is a long term investment and stable solution. Mass immigration just kicks the can down the road. And currently, only two neighboring countries have birth rates above replacement rates: Indonesia and the Philippines. Their birth rates will likely drop below the replacement rate by 2050, in which case mass immigration from those countries to other countries deprives them of a stable future and royally screws countries who were dependent on immigrants who will no longer exist.