As I saw this because of
US Immigration Preclearance Explained, I'll start with that.
airlines that fly to the USA from one of the above-listed airports enjoy a competitive advantage
Presumably, this advantage would be with people who've never tried it.
If a CBP preclearance were to be set up in Australia, it would be more like DUB, SNN or AUH.
i.e. Absolutely awful. I've entered the USA through HNL, LAX, SFO, SEA, ORD and IAD, as well as through preclearance at a few Canadian airports and at DUB. DUB was definitely the slowest of all. A slow, snaking line that filled a room as large as the whole check-in area of some small airports.
If this was to happen this Melbourne Flyer would find a new love for departing out of Sydney.
Given the extra couple of hours you'd need, there would no longer be any morning flights that would safely connect to the morning departures from SYD, so you'd need to fly up the night before, blow a whole lot of time and money for a SYD hotel, and then be up really early. No, thanks!
Then, once you are through preclearance into the US zone, you've got no access to the usual lounges, shops, etc, just to whatever special things are in the US zone.
I could understand ten years ago how people might think the grass on the other side of the fence is greener, but since the US implemented kiosks, customs and immigration has become quick. I'd way prefer to spend 20 mins at the arrival end than have to set aside an extra hour or two at the departure end.