I'd actually suggest it's the opposite - the likelihood of more advanced trainer aircraft is reducing, not increasing. The threshold for what is a viable combat aircraft keeps going up, and therefore the utility of a 'trainer-plus' aircraft is going down. Even for training on Australia, the utility of an aircraft that doesn't have the advanced comms/EW etc capabilities of front line aircraft is very limited - if it can't talk to everyone, then it isn't doing much more than flying in circles burning up jet fuel.
It's the same as arming the OPVs. The threshold of a viable combat ship is going up as well, and therefore the utility of an armed OPV is reducing. It won't be able to do the constabulary work any better, and won't be survivable in an actual conflict, so why spend scarce resourcing in arming them?
Agreed.
There is a minimum level of integration and self defence capability required to make any sort of platform survivable in a modern conflict, this was the reason given for not deploying Australian Blackhawks to Afghanistan and the reason why the equipment that was sent received improvements and upgrades. This is why the 4Sqn PC9 FAC cadre would never have been considered for deployment either.
On the other hand, if 4 Sqn had combat spec aircraft, be they something like the Tucano's the USN were looking to deploy, Hawks with the appropriate systems, AMX or Gripens, then its an entirely different mater.
What it comes down to is cost and the requirements that need to be met, for example the PC21 is capable of taking over some of the tasks that were once conducted by the Hawk suggesting that an eventual Hawk replacement would be primarily an advanced combat trainer, fleet requirements, FFAC, and CAS training / demonstration / development type, i.e. the roles the PC21 can't do.
I also read something recently that F-16 Cs are being cascaded to training wings in preparation for the F-35. This is actually similar to what happened when the RAAF introduced the Mirage, the Sabre became the combat tactics trainer. The Wingeel was the basic / intro trainer and the Macchi the intermediate, with CAC CA31, Jaguar, or possibly F-5, planned as a combat capable advanced trainer to replace the Sabre. The combat capable part is also to provide a more capable and realistic training experience to not just the developing pilots but the ADF elements they support or go up against in training.
I seriously wonder if once the F-35 enters service if we will see the Legacy Bugs and SHs conducting more advanced training and support missions that the Hawk is not up to. If this happens will the RAAF perhaps form an F/A-18F OCU/Advanced weapons squadron in addition to 1 and 6 sqns? This would be very expensive but likely necessary, and if you had what were still effective combat aircraft available, would you avoid using them as such because they had been retitled trainers? Also, when it comes to replacement time, would they look at a long term replacement in that role with something that could also replace the Hawk LIFT capability, probably based on whatever the USAF ends up doing.
The OPV response probably better belongs elsewhere but I would point out that, as much as the RN wants a cheaper Type26 that can be upgraded when required, the options being considered for the RNs Type31 GP frigate are predominantly upspec'd OPVs. Also the OPVs the ADF are looking at now are nothing compared to the OPC 81m Corvette that was meant to replace the Fremantle's (it basically had the combat power of an ANZAC in a smaller cheaper to operate package designed for regional ops), or the OCV originally intended to replace the ACPBs, MCMVs and Hydrographic fleets, which was basically a smaller, slower LCS.
I suppose another analogy is why is the Army procuring Hawkie? Surely they would be better off using armoured Gwagens or ASLAVs? I know the answer, cost, capability and suitability, Gwagen lacks the required capability while ASLAV / Boxer / Patria are over kill.