Not sure it contributes to the situation here much, but in a country not that far away, and in another age, I was rated on, and not irregularly flew, a 31-seat a/c with a PPL.
On various occasions different numbers of those seats were occupied and while it's sufficiently long ago that I don't now recall the numbers, I'm fairly sure the flights were 'legal' at the time. Certainly it was a specific topic of discussion and comments similar to
Office Update re flying a 74 with a PPL came up and, given various factors not worth repeating here, I think that if there had been any significant issue it wouldn't have happened. This machine was >5700kg MTOW, so no longer a 'lighty' either.
I later gained a CPL and, were this in Oz at least, I suppose any technical issues around passenger numbers etc would have disappeared. However, what I think matters is that irrespective of the license I held I was
deemed competent to operate the aircraft type at the time of being rated. I've not made any in-depth study of 'rating' but as I see it the aircraft type - and this specific aircraft - was well known to the examiner, as was my PPL, and that would have to have been taken into account. Said rating did not contain any limitation on seat occupation
ipso facto I could take a group of mates into the wild blue for a jolly.
Coming to Oz; in the absence of any specific, or even implied, seat limitations on PPL holders, and assuming the pilot is appropriately qualified (ie. has a license and is rated, insured etc), and has carried out due diligence (a/c ok, wx etc) then s/he should be good to go. If there is any question over this then it should be up to regulator to clarify that - but from what I read here there isn't, so why all the hot air?
That said, and coupled with this age-old 'paying for flight' differential between PPL and CPL, I think it's long overdue for such things to be reassessed. To me payment in whatever form has little to do with competency, and a license to fly should be about competency - not commerce. If you want to gradate licenses for reasons of experience/risk/competence and for example that say a G3 can fly a/c with max 4 seats and < 2500kg, G2 8 seats and up to 5700kg, and G1 all above that's fine, but who pays for what shouldn't have any affect IMV.
FP.