I was really going to keep out of this but a couple of things came to mind;
The FAA will have no interest whatsoever in what happens in EASA land.
FAR 91.Subpart H, addresses the U.S. commitment to the Treaty. Specifically 91.703(a)(2) states: “When within a foreign country, comply with the regulations relating to the flight and manoeuvre of aircraft there in force;”
Basically U.S. operators are required by FAR to operate in compliance with the requirements where operations take place.
To the FAA the aircraft and crew are fully certified and qualified - which ends their oversight. The fact that EASA are adding their own requirements potentially grounding third country if they feel like it would have to be taken to an even higher level than the FAA and get Lawyers involved. Mainly US pressure curtailed a lot of the Emissions Trading scheme nonsense but the airlines and AOC Operators are not affected by Part NCC.
I really wouldn't hold my breath awaiting a FAA legal interpretation.
I'm not sure of the SAFA check as there is nothing (that I know about) where they tick off the Operators base of operations, which is crucial for deciding if Part NCC applies, for non commercial operations (There is in the AOC section). There will be many thousands of Third country aircraft passing through the EU so how they are going to work out who is based in the EU or not could be quite difficult. Grounding a perfectly serviceable aircraft and certified crew on safety grounds is ridiculous but I suppose could and will be done.
Part NCC does not containing anything specific about licences. However, being old and very cynical, when the Part NCC declaration form is signed
Part of the statement in this states “All flights will be carried out in accordance with the procedures and instructions specified in the operations manual”. Part of the Ops manual is sure to contain some line as to complying with a countries regulations.
There are much cleverer people than me who may know better.
Like a lot of EASA regulation the whole issue is complex and badly written. The problems tend to occur with what is not written.
What a mess, so I'll continue planning my retirement
M.E.