I certainly thought about the ITV Regional News model - keeping in mind that (in the example) Granada keeping its local title was the exception rather than the rule; most just being branded with the region name as (say) "ITV News London". So I'm not sure whether that's more an argument for "Nine News Northern NSW" than the alternative!
However, I'm thinking the other variable in this could be whatever progress Nine makes with Southern Cross regarding local news beyond their noodle updates. If the catalyst of finally switching NBN's main channel to a "Nine" branding was being able to get other regional stations to be branded "Nine", perhaps the news is in a similar boat - that things may be in a holding pattern at Mosbri Crescent until that's sorted out.
If they're able to get the partnership with Southern Cross to a point where there's a localised Nine News on the Southern Cross stations with a similar "opt-out" model cut into the statewide bulletins - and by that I mean similar to what NBN does currently, having the story reads recorded-as-live by the main reader - then there's no reason why NBN shouldn't be following the same model.
That might happen anyway, say, next year if Nine loses patience with Southern Cross over news - but you'd think they'd want a consistent process at each capital city station if that happened, rather than Sydney having to go its own way.