I Think the CAA/EASA should come up with an an official qualification to teach ATPL ground school. In my opinion, you dont need 10,000 hours as an airline pilot to teach aviation theory! It helps, but it doesnt mean you'd be any better than someone who is a natural at teaching. Also not everyone can make it as a commercial pilot or an airline pilot, but they'd still love a career which contributes to aviation.
I think they (CAA/EASA) should follow the example of the FAA and allow those who have a natural ability to teach the theory, to get qualified after obtaining the ATPL knowledge and showing good teaching aptitude. After all, you have JAA CPL instructors, who fly pistons, and can teach both Comemrcial level ground and air instruction with about 500 hours TT. In other words, they dont have a mass amount of flying experience themselves.
Also if you want to be a teacher outside aviation, all you need is a Bachelors (3 years theory study) and a PGCE (Post Grad Certificate of Education), then you enter your first teaching gig at a public school. Aviation theory teaching should be no different, as you are not actually giving instruction in an aircraft.