Japan has 'capsule hotels'. I figured they could be cheap housing for the poor.
Unless capsule hotels somehow magically cure mental illness and substance abuse, they will do little to solve "homelessness", which is a far deeper problem than mere lack of housing.
I have been to Tokyo many times, and have used the capsules. They are nice, and work well when people are quiet, clean, and respectful. They would not work well with typical homeless people, talking back to the voices in their heads, refusing to bathe, arguing and fighting with each other, and vandalizing the capsules.
I have also been "homeless" in America. When I first moved to Silicon Valley, I bought a used van for $4k, fixed it up, and lived in it for 2 years while I built up my savings to buy a house. My employer provided toilets, showers and a kitchen, and gave me permission to park overnight, which was a win-win because that meant I was available when the server crashed at 2am. I later sold the van for slightly more than I had paid for it. Now I am far from a typical homeless person, but I "solved" my homeless problem for a net cost of $0, and any halfway functional person could do the same. The real problem with homelessness is that most of them are not halfway functional, and any "cure" for homelessness needs to account for that.