Why would you do this?
This isn't even an iniative to just legalize bitcoin in all of the countries, is to essentially create a bitcoin nation.
You'll have to face a lot of legal processes, and how are you going to find an uninhabited island anyways? Border disputes are common between big countries and as a country with a maximum population of 1000 people you're going to probably be told off as soon as you settle there.
Plus, legalizing bitcoin is not necessary. Governments cannot ban bitcoin completely. As long as a country is not putting crazy restrictions around bitcoin, i'm fine with it. They don't need to explicitly state that they want to legalize it, in fact a lot of the times legalization = regulation which isn't something a lot of bitcoiners want. Even if they do ban it, trading will just go p2p, and they can't do a thing to stop it completely.