If Jetstar does start regional services it is unlikely to have a major effect on NZ traffic, it would more likely create a new market of travelers out of Regional Airports.
Jetstar regional would struggle to attracted the business market, as with an A320 they couldn't over the same frequency of turboprops. With JQ we would be likely to see services to smaller center either daily or a couple times a week.
Where as NZ using problems is able to provide multiplier services a day, which attracts the business market.