Luke-T, this is interesting, I didn't know that.
This goes even more into the realm of 'plausible deniability' should the IAF fly into the Gulf. The US-led forces certainly would not interfere, and could later say, "as far as we knew, it was a recon flight"
(see: IAF overflights of Lebanon and operations off the coast)
http://www.iol.co.za/index.php?set_id=1&click_id=123&art_id=qw1162156325870B265
For as long as the US owns the airspace over Iraq, which it still effectively does thanks to the glacial pace of rebuilding an Iraqi Air Force and Air Defence infrastructure, IAF missions through that airspace contain a risk: risk that the US will not only say no, but will force the IAF assets into a "squawk or die moment." I expect the latter. Web, there are tens of thousands of USN, USAF, USMC, and US Army professionals who, active, reserve, or retired, are intimately familiar with IFF, squawk or die, and are mineable by anyone in the media for credible answers to that question.
If anyone in US DoD chooses to turn a blind eye to an IAF strike mission over Iran, the US is openly inviting WW III to open up, with a massive political liability on the first move. That plays into the hands of
Iran
China
Russia
Alienates India
Alienates Pakistan
Giftwraps political points to any and every Islamist faction, national or extra-national
Pisses off most NATO governments.
Pisses off Malaysia and Indonesia
Stupid. Worse than stupid, negligent.
An immense loss in the PR and media war, which is a critical piece of modern geopolitical power.
BMD is a better line of thinking.
Hutch: IFF is controlled by Crypto. The hardware is inconsequential, the crypto for Mode IV is the critical element. If you have the hardware, you can make your own crypto. That doesn't mean it would match US crypto, which would mean that a mode IV interrogation would not identify one has being "friendly." (recall two Blackhawks over Northern Iraq who got shot down.) The key question is: has another Jonathan Pollard sort successfully infiltrated US crypto processes and set up IAF with valid Mode IV? Unknown
Squawk or die. That's the RoE I would suggest in this case, in the airspace over Iraq.
Here's a curveball: Turkey lets IAF over fly Turkey and then bomb Iran. Not likely, but who'd expect that? Surprise attack includes "not what I expected."
DR