I am reminded of the old real estate saying that the two best ways of destroying a city are 1) the introduction of rent controls 2) an artillery barrage.

We have seen this sort of populism before when rent controls were first introduced thirty or so years ago.  The effect was to virtually stop the construction of new purpose built rental buildings.  As I recall there was a comparison done that showed that Montreal built 10,000 new purpose built rental units in one particular year and Toronto built about 300.  The 1991 exemption was an attempt to induce builders to re-start the construction of rental units.  Essentially the government gave their word that these units would never be subject to rent control.  Ms Wynne has just broken that moral contract and in fact may have broken a legal contract.  I expect that this will end up in court.