Several decades ago, I was on exchange with the USN involved with the AV-8A, AV-8C and AV-8B programs - note the spelling of programmes!!
Many of the USMC folk at NAVAIR were focussed (blinkered??) by financial considerations, and were not receptive to suggestions of the right way to bring modern - as it was then - technology to the cockpit. By then, I had also flown the Jaguar and the A-7 which were very different from our old GR1/3, and I was astonished at their resistance.
But as with most Marines, their heart - and soul - was with the Corps, and although subordinate in many ways to the USN, they wanted and needed their own air arm, and would do nothing to jeopardise that essential operational need.
So it was a real game of politics, even then. Inter-service politics. We all know how that plays. And probably little has changed.
The F-18 is clearly a great machine. But if they can engineer a way to use our regrettably unwanted GR9/9As to supplement their AV-8B fleet, then I am sure they will do so - as long as they meet the need to support the marines on the ground.
Politics will be at play here - as will financial considerations.
But with delays to the F-35, the need to provide effective organic air support for the grunts on the ground will be the driving force.
I hope they do stand up a couple of squadrons of AV-9As - or whatever they call them.
As to supporting them - we are still allies - aren't we??