There was a great episode of the Planet Money podcast a few weeks back that talked about boarding houses https://www.npr.org/2026/06/10/nx-s1-5851902/housing-afforda... they're apparently illegal in most places

Large parts of the floor would be illegal to hand to anyone due to lack of natural light: They are only reasonable for offices because most of the floor doesn't have full walls, or said walls are transparent. They are also in locations where you might not want to live anyway, as there's minimal commercial support around the building for the services you would need if living in a weird, limited apartment.

It's a bit like how suburban commercial areas are now in trouble because there are fewer companies interested in the big box anchors, and without them many a strip mall stops making economic sense. But there at least the anchor is just a big empty box, not an 8 or 9 digit investment.

In the 2010s Seattle briefly legalized SRO-like "pod apartments" of 300-400 sq ft, and several were built. A friend of mine rented one for several years and it was fantastic. But nothing makes NIMBYs throw a shitfit like the word "SRO" and they were eventually made illegal again.