I am also aware that the CPL knowledge is an ICAO requirement, but as I already have that with my FAA stuff, I can't see why this can't be credited, to allow instruction towards PPL. Makes no sense.
If an EASA CPL holder with EASA FI certificate wanted to teach in FAA-land, would they be credited with FAA CPL theoretical knowledge? No.
Therefore a pilot who is not trained to EASA standards will be sub standard and dangerous when flying in air within EASA authority.
Under EASA you can add a FI certificate to a EASA PPL. Someone instructing under EASA wishing to obtain a FAA CFI would have to convert their EASA PPL with FI certificate by completing the process to obtain both a FAA CPL
and FAA IR to then be able to add a FAA CFI certificate for airplanes; both the FAA CPL and IR requirements are over and above ICAO Annex I requirements. That's without mentioning the additional TSA and visa requirements...
ifitaint...