Further to Reaper's comments, I also think part of the reasoning behind past decisions which permitted purchase of just about anything, imported or local, was to do with running costs and availability of suitable vehicles for specific purposes. In years gone by, when fuel prices were much more volatile than they are today (yes, Priscilla, there have been worse times than the present), fuel consumption was a major determinant in vehicle purchases. I can well remember when Toyota Coronas were purchased as patrol cars by NSW Police because Holdens and Falcons of the day were too thirsty. More recently, vehicles such as Foresters were purchased for specific duties because the locals didn't make a suitable alternative.
It's worth considering that when it comes to high speed vehicles, local cars remain king for police use and have been almost the exclusive use, with certain periods of digression back in the 80's and 90's when a hi-po import might have been used. If you look at the UK police, you find they don't use British vehicles for their highway patrols - generally the vehicles seem to be BMW's.
Even today, we will find that government authorities will continue to purchase/lease imported vehicles because the local industry doesn't manufacture a suitable alternative. The new edict won't change that. It just means that a few thousand more Holdens, Fords and Toyotas will take up government duties than might otherwise have been the case.