I think the problem with that is that it needs an objective metric applicable across the EU. Designating Cambridge a mountain airport in an attempt to keep the Dutch out (assuming the NL didn't designate any of their own) would be anticompetitive and would probably raise a few eyebrows at EASA. To allow the UK to arbitrarily designate the airspace in which the IMC rating can be used would discriminate against the guy in France who would also like to train people to fly in IMC in less crowded air closer to home but can't because the DGAC won't designate it as IMC-rating-proof.
It would be good if a way could be found not to throw the baby out with the bathwater of EASA's standardisation.
I believe the IMC-rating's success story underpins the safety case for the attainable IR, which should offer better privileges than the IMC rating on barely more flight training. While adolescence is often a painful time, one could claim that the IMC-rating baby has grown up.
