Until the FAA IR is done by check instead of rolling experence requirements to keep it current there will be no crossover.
Apart from that there is still the problem that alot of the tolerances are tighter for the european IR.
I think heading is +-10 FAA EU its 5deg
They are aloud 3/4 scale deflection we are half scale.
And speed they are 10kts and EU is 5knts.
Then there is the theory requirements.
Which is why it was only ever acredited IMC rating.
Where as the European IR is the same what ever flavour of license you hold.