the fibre is going to do little other than allow New Zealanders to watch HD re-runs of Shortland Street.
On the other hand, it only takes one or two New Zealanders to download content from foreign servers and mirror it, through bit torrent or other means, to everyone else in NZ.
Transfer caps are the norm here - we used to have zero-rated national traffic but that was phased out by all ISPs some time in the early 2000s.
You're absolutely right, if all our piracy at least was kept on-shore via DC++ or similar, it would likely cut demand for international bandwidth in half (the same goes for probably any country). As it stands there are substantial caching servers employed by every ISP for most high-traffic static content (Youtube, Steam, onshore broadcasting...)
On the other hand, it only takes one or two New Zealanders to download content from foreign servers and mirror it, through bit torrent or other means, to everyone else in NZ.