RNZAF already has T-6Cs, which can be armed with rockets and Paveway LGBs. For COIN or FAC work, they should be sufficient. What NZ lacks is fast jets to deal with incursions from enemies' fast jets.
JTAC training and accreditations using the T-6 platform are plausible however the NZDF employment contexts for counter-insurgency are well off the threat radar in our AOI (South Pacific and territorial New Zealand) which fortunately are peaceful civic societies and do not warrant such specialist investment.
The employment context of fast air in the NZ context was never about local air defence to deal with incursions from enemies' fast jets (and to be honest that is still the case) but CAS, interdiction and maritime strike as part of a expeditionary contribution to a coalition force.
I do not want to damper enthusiasm however but reconstituting an air combat capability within the RNZAF will mean we would have to look forward to what is ahead of us rather than simply replay what we did when we flew A-4"s and Canberra's post war. One of the capabilities envisaged downstream within the employment context of the cancelled F-16's was AN/ALQ-131 and if evolved EW would have emerged as a more prominent capability within the platform and NZDF operations.