There are quite a lot of prejudices here, but this one
What could be added on the IMC rating syllabus to make it a IR acceptable one ?
It is not something that should be added, it is the whole spirit of the thing that does not cope with the requirements.
1) Flying IMC intentionaly should require an IR, which means a full IR training and understanding (only the ground school part should be improved : a lot of questions are completely useless).
So the whole IR syllabus should be the one you are taught before flying IMC intentionnaly.
If you think an IMC rating is enough to handle IMC, so that means you think that the IR is completely useless.
is the real problem.
All the time there is the total complete attachment to the full IR for any flight in IMC, little progress is likely to be made in Europe, because of the army of people who want to keep the IR just like the old days. Actually "old days" is not a good description because the Euro IR was much easier in the old days; easier on flying and far easier on the ground school.