The new proposed Zone reforms will be gazetted on the 1st of July 2013 and will be available for review on the 17th of July.
When they are adopted into the Victorian Planning Proivisions a motor racing track will fall under leisure and receration within Section 2 of the FArming Zone. To obtain an approved planning permit you would need to provide evidence of consistency of what is proposed in relation to the Zone provisions and any other applicable land controls, Overlays etc.
It appears the new zones will make it a discretionary use, but councils will most likely still scrutinze an application for one very carefully.