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.

SROs done right would be such a huge, easy win for so many cities. When I was fresh out of uni, I rented rooms for cheap with all utilities included. It was great, given the price.