Though I'm not familiar with the Austrailian system it seems intersting that an offset could cause the ATC computer's tracking algorithm to not detect that the aircraft was the one on a nearby planned route of flight. In the terminal environment in the U.S. (and I think enroute too) the secondary radar (beacon) gets a target report, correlates with the primary target and matches them up if they are at the same point in space, tags the data block to it and updates the track file that the display is made from. Uncorellated targets are worked on the next time around and if still unresolved taged as unknown ID speed and alt unknown.
The Automatic Dependent Surveillance bit is very attractive to the beancounters until you tell them that it is only as accurate as the aircraft's knowledge of it's own position and that though it has been made to work in tests it hasn't been used much in the real world, unless you count United transPac to Oz with FANS, which I understand was a big bust.
Combine with that the fact that the data link standards are not set (1090, VDLMode 3, VDL mode 4, etc are possibles) it will be a long time before anything like this can be really operational.
It would be very interesting and instructive to gang a bunch of simulators together with an ATC and try RVSM, ADSB, Free Route and other things in a virtual world. though it would cost millions it would be a lot cheaper and safer than the possible bent metal, let alone wasted money, it there are some unexpected fatal flaws in the concept.