> Every demographic crisis involving low birthrates is an immigration melting pot waiting for the population to get desperate enough to change policies.

Unless people accept the reality that perpetual growth is impossible, and that the economy will shrink as the population does. The UK austerity years provides a decent example of such a "managed decline", albeit with more immigrants, but that's not assured when the next conservative government comes to power.

Changing policy to admit more immigrants is easy. Changing culture is hard.

Depends how long they wait. Unless something changes in the next decade areas producing excess population are going to be in demand and they may find it difficult to attract people quickly enough.

maybe in the west, but asia is pretty racist, and the japanese have resisted until now pretty well. we'll have AI before they'll capitulate for any real migration