Today, Maoris in New Zealand make up about 15% of the country's population. They are relatively well off, although somewhat societally disadvantaged. On average, Maori are a little poorer and shorter-lived than other New Zealanders. Nevertheless, they are a powerful voting bloc and have strong rights based on the 1840 Treaty of Waitangi, which remains in effect to this day.
Your challenge is to make the New Zealand of 2012 a Maori-majority state, while still keeping it a British colony well into the 20th century, just as OTL. Bonus points if you avoid structuring the country as a white minority ruling over a Maori majority (a la South Africa) and extra bonus points if you make the country even richer than it is today (difficult, since it's a very rich country already).
I've always had an affinity for New Zealand, and I'd love to see where you guys take this!
Cheers,
Ganesha