I can't see how EASA could remove the IMC privlidiges for those who already hold the rating, without there being a riot! Has such a thing ever happened wihtout those being affected, being given grandfather rights to something else?
I would say that the three most likely senarios are
1) Those who already old an IMC rating keep the privlidges within UK airspace, but noone new can get the rating, or
2) EASA introduce it's own IMC rating, and UK IMC holders are given a free EASA IMC rating in return for their UK one, or
3) All those with an IMC rating loose the IMC rating and are given a free IR, but with the conditions that it can't be used in class A airspace, can't be used outside the UK and whatever other conditions are required to ensure that it's basically the same as the existing IMC rating.
I think there is plenty of precidents for any of these options, but none for the complete withdrawal of privlidges without any replacement.
If an IMC rating was available to me, I'd do it straight away, and wouldn't be worried about what might happen with EASA. I'd do this because
a) I agree that it would be a good stepping stone to a full IR, and
b) there is a very good chance I'd benefit in some way in the conversion process, and
c) It's an extremely useful rating to have now.
dp