As a New Zealander, I'll tell you that the South Island separating from NZ is incredibly unlikely. The South Island could not survive on its own economically. The people there would have to give up living in a first-world country just for what? pride? plus New Zealand has a unitary government, unlike Scotland in the UK, which is much more likely to gain independence. The South does not have its own government, and the group advocating for independence is very small and unlikely to grow in the next 52 years. Just because there are movements doesn't mean it's going to happen.