Plans to extend the runway in NSN have been on the plans for quite some time with the land to the north already purchased.
I doubt you would see NSN as an international airport but once the runway/taxiways were extended and screening in place which has also been taken into account with the new terminal currently under construction there would be no reason why AKL/NSN/AKL jet ops could not take place .
The pay off would be frequency 1x jet at the expense of 2 x ATR flights so not as many flights per day to and from AKL/NSN, WLG and CHC would stay turboprop routes?