owen,
Can you point to me where, in AD/ENG/4 you can use engines on condition, now, for Charter or RPT.
I don't see "commercial operations" under 119/135/136 being any different to the present situation, Part 137, Ag, is a different matter.
As far as I know, the long and successful history of life extension programs for Charter and RPT piston engines have been ignored and have all been extinguished.
Tootle pip!!