Quite right however
Consequently, the 'No aerobatics' restriction attached to newly issued FI ratings is entirely worthless as the individual can, quite legally
this actually places a limitation on the holder of the rating and legally they cannot give aerobatic instruction whereas a person who does not have such a limitation can.
The reason you cannot hire SLMGs is because they predominantly operate on a Permit to Fly; to hire it out you will need to maintain the device to public transport standards; somewhat more costly.
The status of a licence that may have expired or whatever, is completely irrelevant; the point is that any person who has held a licence is not an ab initio student therefore, the extra safety precautions that are put into place by requiring a Flight Instructor to go through an AFI/FI(R) apprenticeship do not apply.