Having an RPC with nav endorsements does not mean you should just be issued a PPL - you have to meet the CASA standards for a PPL, (the typical PPL training syllabus is around 30 hours on top of RPL standard).
I think for PPL you will need for flying side (would also need PPL(A) exam etc):
- to be at RPL skill standard in the VH aircraft (ie would need assessment flight)
- 2hrs BIF
- at least one solo navigation flight of 150nm with 2 landings away from departure field (I assume this can be completed in RA)
- to have a minimum of 5hrs solo nav time (I assume can have in RA)
- pass a PPL flight test (which would involve flight into controlled airspace or simulation of controlled airspace). It would be unlikely for a school to do a PPL flight test without making sure you are at the required standard so you would need a nav assessment flight before the test.
standards for RPL and PPL would be in part 61 MOS. The GA school will have to sign off that you are at those standards.
My opinion - I would think the hours needed would be highly individual.
It depends on the pilot's ability to meet the CASA competency standards in the VH aircraft being used and on the standard of RA training.
I could imagine at a minimum, one pilot could hop into the VH aircraft and do an assessment flight, acing it and demonstrating appropriate ability at RPL level in a 1 hour flight, then do a navigation assessment flight (CTA, lost procedures, diversions, low level, operate at CTAF and controlled aerodrome) of say 2.5 hours and ace that (would be busy flight). Then on the basis of that do a PPL flight test of 2.5 hours (which they pass) so total around 6 hours or so?
If the student is flying an RA aircraft similar to the VH aircraft and has been taught well, this should be achievable (there are some RA aircraft that have equal or higher performance than some common GA training aircraft).
However, another student with same paper qualifications might need remedial work to get to RPL standard in the VH aircraft, maybe another 5 hours because they are just not up to the new aircraft yet, have not been taught stall recovery well (1 hr remedial), have trouble landing the new aircraft (3 hours in circuit), have poor crosswind technique (another 2 hours again) etc.
After this, they then get caught out on the nav flight because they are way behind the aircraft and have been relying previously just on an EFB for navigation and have no basic fall back nav training (and maybe stuff up their controlled airspace entry, cannot maintain altitude and heading tolerances and cannot do a diversion without an EFB to help). So need another 2x2.5hr remedial navs before their flight test meaning now a total of over 12 hours This more likely if the student has been flying an aircraft with significantly lower performance than the VH aircraft or have been poorly taught. It may even be more.
Sure, not all students will need a lot of extra time but if they do, it is not always down to their lack of ability, just their previous training and aircraft experience. It can be hard to break bad habits.