It’s yet another demand side attempt to resolve a supply side issue, while ultimately forcing new market participants to spend far more for the same home.
It’s a hack attempt to “solve” a problem from the wrong angle and it will, if it happens, be yet another intragenerational wealth transfer that largely older recipients can plow into equities at the cost of added years of labor for those younger than them.
50-year mortgages are the shrinkflation of debt instruments. Lower monthly payments, but from lower equity accumulation. And the lower payments could just get partially capitalized right back into housing prices.