There will be Sanctuary districts. They'll just be dead and desolate small towns. The city land is too valuable to waste as a sanctuary district. Anyone too poor afford the rising rents will just be arrested for being homeless and dumped in some small town around an oil refinery, paper mill, or some other leaking chemical plant that has made the surrounding land too toxic for farmland, which is all owned by bill gates and patrolled by armed security. The farmland is worked by sanctuary district day laborers for a pittance.