Unlikely to happen.
One card for use in all New Zealand public libraries won’t happen without significant buy-in across New Zealand.
A significant commitment of time & resources from all local government/authorities would need to happen before this project would become a reality. And not all public libraries are overseen by their local government authority, some are run as trusts (Horowhenua Library Trust) and other are run in partnership with other local institutions (Puke Ariki).
Despite significant cost savings, advocacy ‘wins’ with greater collection of useful and usable data, and an improved, synchronised debt collection process, I don’t see this type of project happening before I retire.