OK, then lets look at a 'similar' sport/recreation/qualification.
In the world of SCUBA Diving there are recreational divers and commercial divers.
To become an instructor of recreational divers through one of the many (RAA like) agencies one has to have logged 100 or so recreational dives.
To become an instructor of Commercial divers one must be a commercial diver at least at that level (there are multiple levels and ratings). A Commercial diver cannot normally log commercial dives towards a recreational certificate because the two worlds are a chasm apart.
I would suggest the same of commercial piloting. CRM relates only tenuously to student instructor interaction. The PPL has no interest in profitability, nor in most cases complex aeroplanes (not that a 200 he CPL has much of a clue here either).
I have heard no argument that defines anything a CPL has that makes him or her the rightful 'only' instructor candidate. There are arguments that PPL experience doesn't coun't, but are they valid??? I don't know that there is much difference. However I did suggest NVFR or aeros to show the PPL isn't just 'basic'.
So, I remain all for it. I think it would breathe new life into aero-clubs and give a viable alterntive to the 'K-Mart' pilot factories springing up.