Even more tenement type layouts would be spectacular for increasing stock, but this is just half of the problem. It's all entirely dependent on reducing the level of greed landlords can get away with today.
This isn't really true. The easiest technical solution to the problem of ISPs using your wifi data is to simply use your own WiFi router which does not send the data to them.
Merely extending flood insurance is not the solution. There should be a national pool of money available for climate disasters that can be disbursed every year to the major disaster incidents. This money can be raised from corporations or insurance companies or executives or any other pots of wealth.
Perhaps as an alternative there could be a national fund with risk adjusted fees that is mandatory in cities that receive services.