The way the system is organised at the moment there is nothing to stop anyone to start teaching theory on his/her verandah. We once had an organisation called the Australian Association of Ground Training Organisations' (AAGTO), of which I was a foundation member. That organisation tried to set up some form of licensing requirement for ground instructors but it was forever put in the 'too hard' basket. Even something as simple as a requirement for theory instructors to be registered with AAGTO to allow some degree of self governance was never pursued. So, if you want to be a theory instructor, you just hang out your shingle and start. You don't even need to have any pilot licence at all.