Personally I would like to see a ban on all read-backs in Australian airspace. There is far too much superfluous radio chatter and when you see that at least 50% of that is read backs you can understand why. With modern VHF radio systems that allow crystal clear reception then if a pilot does not understand an ATC transmission he simply asks for a repeat - not a read back just to see if he has got it right or wrong. The current AIP read back requirements have quadrupled over the past 25 years and my guess it is now more a legal arse-covering exercise rather than because something may not have been understood.