The problem is economic and political. Witness the riots that took place in France when they even talked about raising the retirement age. If population declin

The problem is economic and political. Witness the riots that took place in France when they even talked about raising the retirement age. If population declines that much, retirement will become structurally impossible for anyone but the relatively wealthy. Other types of social safety nets will also collapse, because at some point young working people will just balk at the tax burden they'll have to pay to support them with a shrinking cohort of workers. AI and automation could cushion the blow to some extent.