Would be interesting to see if passengers on yesterday's flight used the D sticker system to board their QF flight from the INTL terminal
I suppose an issue could be I>I transfers, however, there are ways to resolve that issue. For instance, in the United States prior to 9/11 international arrivals not entering the US were sequestered into a holding area where they would be escorted to their plane by border officers when boarding commenced. Now obviously that facility has gone away, however, for those with Global Entry or Mobile Passport the process is still very fast having flown into LAX, SFO, HNL and a number of other US ports from abroad. Like we're talking 5 minutes here which barely makes a dent anywhere. Now I know, Australia isn't a world leader when it comes to processing international passengers (due to its emmigration and immigration process) but the US has shown it can be done.
In defence of segregated domestic and international departures (and I can't believe I'm making this defence), there are some merits. Specifically I can think of flying into Vancouver from Australia and not having to clear security. Instead it was a quick iris scan for immigration and I was dumped into domestic departures with my bags being forwarded on to the final destination of Saint John. This system, called
One Stop Security, made possible through an ICAO annex, is available at a number of Canadian airports including Vancouver and Toronto.
So I guess what I am trying to say is please make the process smooth one way or another. If you wanna do segregation there should be 0 connection process. It shouldn't be like the nightmare that is Changi where you have to show up to your gate 30 or 45 minutes early to clear security. You should be able to board your plane or go to the lounge without worrying about security or immigration. On the other hand, if you want an unsegregated experience as is the case like the US, make the process of immigration and security painless as they have done for Global Entry members.