In Toronto I think we'd love this idea for the same exact reasons. Our city was amalgamated from several different cities in the 90s and most people regret the decision because citizens/politicians from the more suburban areas have different motivations than those that live downtown (especially WRT driving vs transit). The infighting over the years has caused many delays/cancellations in our infrastructure to the point that transit has become possibly the #1 problem for our city. I can't compare the situation to Sydney but aren't smaller jurisdictions generally more nimble?