rmcdonal
That's true, but the ONLY land available for such a venture is well beyond the current fringes. That it might also be clear of aeroplane noise averse neighbours is an added bonus. The primary consideration though, is cost. There simply is no more spare land closer to the rest of Sydney.
It keeps filling up, and the NSW pollies are too frightened of backlash from people sitting on 5 acres semi rural blocks (who are licking their chops in anticipation of a rezone & subdivision) to stop the sprawl. That's why it would have to be done ASAP, before the land has all gone.
Some sort of buffer zone (a mix of parks, golf courses, playing fields, light industry) would also have to be included. So rmcdonal I agree, you'd have to do it in such a way that 15 years later NIMBYs couldn't force it closed.
Cheers