The upper limit is when the middle class has the entirety of their retirement accounts invested in their homes. As long as investments in primary residences continue to maintain their unique tax advantages, people will keep dumping their life savings into their homes.
And then sell to someone who is willing to trade away $ sufficient to retire on for just a home. I'd say this seems crazy but we're already there. People in SF and NY sit on homes and keep working when they could sell the home and jet set for life.
