Interesting that the CRI single-engine entry requirement is 300hrs!
I think the whole CPL thing is a bit of a red herring. As someone who has done the CPL exmas purely to get an FI on my PPL, they were hard work and a pain, but I really can't see how someone who thinks they can't do them due to motivation/time/money could manage an FI course due to motivation/time/money etc... I think the key to all this are the standards demanded in the air and on the ground on the FI course - pretty high in my experience, and any 'bad' PPLs will soon find themselves doing more than the 30hrs to get to pass standard. Moreover the standard demanded by club / schools of their FIs during normal ops and at renewal time - how many CFIs fly now and again with their FI(R)s to check their instruction and mentor their instructional development?? Someone could do an FI course and only have to have someone see their instructional technique once every 6 years after that (how many exercises etc.. will that cover? Any nav in that??)