Now that I'm away from my tiny smart phone, I have a keyboard to speed things up.
Here's why I believe the USMC will not operate GR9A as a GR9A:
1. The aircraft has diverged so much from AV-8B standard It would need to be operated under a UK RTSA (or take years to transfer across at significant $$$)
2. It has a UK EW system that would need to be supported and Pre Flight Messages produced. Releasability and technical transfer issues abound.
3. It has a different cockpit layout.
4. It has a mission planning system that is unique to the UK and would need to be fired up and supported.
5. The aircraft only has 2 buckets for expendables as opposed to 6 in the AV-8B; does this mean the US is now committed to the TERMA pod weighing 600lbs - unlikely as this pretty much precludes the carriage of anything else (such as a weapon) at sea.
6. There's no gun and no piping for it.
What was is exactly that impressed the US at Red Flag? Was it the aircraft or the capability (HMCS; Sniper; PW4)
If the latter, it would be much cheaper to cut up the GR9s into parts to support a higher AV-8B FE@R or assure a better AV-8B FE@R for a longer period of time and pay the much smaller cost (than items 1-6 above) of integrating better capability.