The business class seating is remaining unchanged on the A320s - it's actually pretty good seating: 2 rows of 2+2, 42" pitch, trimmed in nice soft leather - but on the Brisbane routes it is being sold as Y+ while on other routes (for now) it's still J, with all the associated trimmings. There are a few other A320s coming online in Freedom Air config with 40" rather than 42" pitch (and 30" rather than 32" down the back ).

For the time being, NZ has not announced that it's discontinuing J class on any Tasman routes other than the Brisbane ones. It's also worth noting that:
1) There is still 1 AKL-BNE-AKL service per day with J class, timed to connect to NZ's USA and other international services
2) Some AKL-BNE-AKL flights are operated by the brand new 777 with swanky Virgin-style business class suites, but still sold as only Y/Y+, so I presume this means you might be able to get a lie flat bed as your Y+ seat - not bad at all
3) NZ's trans-Tasman Y class isn't luxurious but it's not too bad: the A320 seats are actually very comfortable and decently spacious, (except the Freedom Air birds, I presume), there is main screen entertainment (movie plus shorts), and there is still free food (small but generally tasty meals, cold at lunchtime but hot at breakfast and dinner) and alcohol (full bar service).

As Al B pointed out, most flights are short (around 2.5 to 3.5 hours flying time) so it's questionable whether it is worth re-routing through AKL (where the international to domestic transfer can be quite slow and painful) just to get the J service.