Gallop reports New Zealand is third-ranked in the world potential net migration indices. Global survey nets for each country how many folks say they'd like to leave, how many folks would like to move there, and takes the net as a fraction of overall population. We could see a 170% increase in population, by these figures. And we have plenty of room for a doubling of population so long as they don't all want to be in Auckland.
Sixth from the bottom of the list: Ethiopia, where half the population wants to leave.
And I cannot find a single Ethiopean restaurant anywhere in New Zealand. Closest one: Melbourne.