As I used the 'Edit Voicepack' application to add in many new callsigns etc I switched to the ICAO terminology which is about 80% accurate.
I agree that FSwhatever should include these standards as an option to FAA.
They are striving for realism, this should be relatively easy to implement
Using EditVoicepack to change to ICAO standard is an insane amount of work for me. We are not talking hours here, we are talking many weeks full time. This is why I think it is important to get it fixed in FS itself.