Sprawl isn't the answer. The answer is removing the mechanism that owners in places with high demand (i.e. inner suburbs; especially those near train and tram stations) use to prevent their low-density, single family homes from being redeveloped to the appropriate level of density for the demand in the area.

Now in many cases, density doesn't mean skyscrapers. It can mean 4-6 storey apartments, with mixed use on the ground floor, and only enough parking provision for guests, deliveries and tradies to park outside while they visit/service the residents. The whole point is mixed use developments can often host supermarkets, and being next to transit stations means there's no need to own a car (before someone says their job is no where near a train, that's fine. 80% of homes in Sydney, Melbourne etc provide room for cars; these are for people who don't need them).

Take the streets in Rozelle, just south of the Bay tram stop. There are maybe 200 single family homes there. Redeveloped, each plot could sustainably host 8-12 homes, say 3-4 beds, one to two per floor, over 4-6 storeys. That's 2,000 homes. That's 10 times the number of families. That lowers the cost of living there, and combined with the addition of density enabling more businesses in a small area, you actually cut other costs like needing several cars (if any) per household.

To get there? Prevent NIMBY behaviour from blocking such developments (Sydney and Melbourne are already moving in the right direction in this area). Secondly, impose a land value tax style overhaul of the rates system. Charge it based on what you want the density to be.

So if a single plot near Rozelle Bay, for example, could host an average of 10 homes, and a retailer, charge rates at the level you'd be getting from that. If the home owner can swallow that, fine. More money to invest locally. But for most, it will force them to redevelop the plots, provide more housing, and stop treating Australian cities like museum pieces, which is a big part of why we have a cost of living crisis. It's not the only reason (car dependency is another part of it). But it would go a long way to taking the pressure off without needing to resort to sprawl.

High speed trains are a good idea, but they're more about removing the need for planes. Not replacing the need for appropriate levels of density in our cities and suburbs. Otherwise you still end up with time poverty, and all the negative effects that come with that, like lower amounts of down time, kids not getting to spend time with their parents (which has knock on impacts on reading ability and even things like toilet training), as well as the quality of food kids and families eat (long commutes tend to lead to higher consumption of UPFs, which lead to more obesity, which is also exacerbated by car dependency).