Hence my STRONG instincts would be to ditch saving the IMCR and put all my efforts through the European Courts on the creation of a more easely achievable PPL IR for NON professional pilots.
I think you should get top notch legal advice before even thinking of going down this route.
The legal route has been tried, in certain isolated cases e.g. where the CAA has not followed proper procedures and discriminated illegally against somebody. I know of a few pilots who turned up to a medical with their solicitor... but this was in effect a threat of a judicial review. That is not the same thing as forcing through a demand for some kind of instrument qualification. IMHO this would not work because of the long established precedent where you have the "we wash your hands of you" VFR, and you have IFR for everything else.
What might work is a legal challenge to the stripping of pilot privileges by killing the IMCR. There are various precedents for that e.g. you have spent £X getting it, with a reasonable expectation of being able to keep it (by a continued meeting of checkride standards, medicals etc) and now it is being taken away.
Look at the history of previous pilot paperwork under the CAA. They have always tried to grandfather everybody into something. So if you were an old PPL instructor from the goode olde days, you got a BCPL. CAA CPLs got a free IMCR too. And so on.
Now, this extensive "we never leave you to hang out to dry" grandfathering could be because the CAA really love their customers (I am not being sarcastic) or it could be because they popped down the corridor to their legal dept and were advised that if they do such and such they will get sued. My guess is that
both are true.
Under EASA, there is a threat, for the first time ever, to hang people out to dry, with no compensation.
I made some enquiries about this stuff a while ago. An Act of Parliament allows privilege stripping to be done with impunity, but a lesser body making the decision (e.g. the CAA making it in-house) does not give immunity from litigation. So if e.g. the CAA had booted out FAA licensed pilots, they could have been sued. But if this was done by a change to the ANO, they would have been protected.
AIUI, EASA regs have the same authority as the UK Parliament, so I don't see any avenue for a legal challenge on that one.
I am not a lawyer, of course.
The other side of this is: who is going to do this dirty work? AOPA UK are 99% VFR, despite most impressive London premises are dramatically under-staffed and clearly unable to take on anything big. They do have a lot of corporate members (schools) but the IMCR training income has dwindled in recent years anyway (see the tables published in FTN).
The best way IMHO is to try to preserve the FAA scene or to ensure a fair grandfathering from FAA to EASA (FCL and certification) and the best way to achieve that is the same as ever before: go for maximum political damage. So, make sure that every TP and jet operator knows what is coming. Currently, I guarantee that 99% of them haven't got a clue. I am contacting the Marketing VPs of the manufacturers right now, but there are all the owners which need to be done. These people have powerful contacts.