Whichever they do get I know it will be a domestic spec. No IFE, no business class, no winglets (if NG) and probably not ETOPS maintained.
Surely as a minimum they would have to maintain a 50/50 split of configurations. if it is going to be a 1 type fleet to cover domestic and Trans-tas/PacIslands, then I doubt very much they would withdraw services such as Business class, IFE etc. That'd be very backwards and very un-AirNZ-like . Maintaining the fleet to a stand config would provide greater flexibility for unsched maintenance etc.