unless like in some countries where it already exists (France) the aerobatic instructor rating should be converted,
There is no need to convert anything, either a FI or a CRI will be able to teach for the aerobatic rating, provided they hold it themselves. As it is not planned until 2015 there is some time to go before any course emerge.
Interestingly, there has never been a syllabus for the SE CRI (SE) rating! JAR-FCL Part 1 only contained a CRI (ME) syllabus which is all about asymmetric operation. EASA simply copied the CRI (ME) syllabus into Part FCL and because nobody at EASA knows what they are doing, they did not notice that there is no syllabus for the CRI (SE) rating. Most FIC providers ask the potential CRI what they intend to do with the rating and model a course around those basic requirements, adding it to the 25 hour teaching and learning package. You can't teach much in 3 hours flying. As the primary function of the CRI is to train for additional Class or Type ratings, the syllabus will always be orientated to that aim.