that means an FI(A) with aerobatic rating will be enough ???
That is correct. In the UK, there is an aerobatic add-on (or rather limitation removal) for instructors, but there is no aerobatic rating for pilots, so legally, they did not need to be an instructor to teach aerobatics. As you say each State has different arrangements that are National, there was no JAA aerobatic rating for a pilot or an instructor. As EASA now has an Aerobatic rating for pilots, the biggest problem will be working out grandfather rights for those who currently do it with no rating. Until the rating is finally establish, there will only be a limited demand to train for it. Anyone who qualifies for this rating under grandfather rights and is also an instructor, will be able to teach for it. There is no specific Aerobatic Instructor Qualification under EASA, just the assumption that if you hold the pilot rating and an instructor qualification you can teach it. Not a necessarily safe assumption!
Some books
here