30 year mortgage rates are around 3.65% this week. So if a buyer puts down 20%, that will be around $259k in interest over the life of the $400k loan, putting t

30 year mortgage rates are around 3.65% this week. So if a buyer puts down 20%, that will be around $259k in interest over the life of the $400k loan, putting the total interest at half of what you said (~$760k total the life of the loan versus $1 million). While certainly the US population is aging and slowing in growth rate, I have not seen any predictions for a population decline by 2050 or even 2100. You are right that further urbanization is expected and buying outside of cities may not be a good investment.