The state in this case is Louisiana.

I think GP might be using "state" in the common international English definition, e.g. state in the sense of "sovereign state" or "city-state", not "US state". I would agree with you though that any US government actually implementing the idea today is hard to imagine, but I can easily imagine that after 2 other cities suffer a climate-related disaster first, then there will be the political will to bring a program like this to life. It's a creative policy idea, I love the thought that was put into this.

Louisiana is just the state with a major city closest to the point of it having to be abandoned. There will be more that follow in other states, such as Florida.