Slightly OT - AUS is getting it's second (seasonal) TATL next summer - http://airlineroute.net/2015/07/15/de-aus-jun16/ - Condor twice a week to FRA so BA will have a little competition.

As far as testing the 789 on the LHR-AUS route it is 'expected' sometime in September after the delivery of G-ZBKA with some sort of alternating between LHR-AUS and LHR-YYZ probably similar to the LHR-ARN tests back with the 788 in 2013.