This is my gut reaction; but, then I've been looking at Barcelona — which has analogs in New Jersey and Chicago. In these three cities there used to be significant housing stock that could be affordably purchased by low income families. (These are row-houses and 2x3s, etc.) In Barcelona, for instance, a unit could be purchased by a single family earner in about 5–8 years. What happened, over time, was that a neighbor would move out, and so a tenant would buy the neighboring unit to "expand" (remember: the units are
cheap). Over a period of 25–30 years a relatively modest income could be used to gradually buy up an entire unit. Then, at the end of that period the whole unit would be sold as a single family dwelling. The problem is that what was
once 6 modest (affordable) units, is now a single fantastically expensive unit. The economic model that covers this is a deflationary zero-sum market. (Pretty much all real estate is going to fall into this trap without very careful consideration.)
I think this problem is much, much, much harder than most people think. Almost every single society — except for Japan, AFAICT — is getting hit by this issue, but each in their own, novel way, that covers every possible "obvious" solution.