Maybe the real reason for a shortage in FI's could be that the progression (eg.to a IRI) has been hampered by EASA. Not my view, but one offered by a mates who instruct.
I also initially thought that you could instruct under easa with a ppl and completed cpl theory. Now it seems, judging by an advertisement in the back of a popular GA Magazine, that you don't even need the cpl theory either.
Surely this must cause a few problems in that a cpl/ir holder, possibly with some debt, would rather head off to Africa to break into the job market than compete with a ppl/Fi with no debt for the same instructor job. A matter of flexibility/ability to do the job for peanuts is where I am going with this.
Coupled with the time, cost and effort to train and study for a cpl it may feel to some budding future instructors that the route to the FI rating seems watered down. Not the FI rating itself, don't get me wrong.