This will at some point need to be addressed, but likely won't...

This will at some point need to be addressed, but likely won't be until global population keeps falling. For the time being immigration is being used as a developed world substitute for child birth. One possibility is differential taxation where people with children under 18 receive a discounted tax rate. So the person on a marginal tax rate of 35 cents in the dollar gets a 10 cent discount and pays only 25 cents. Make the economic incentive large enough, and people will have children. The politics of getting there might be problematic.