For now, BR is going to use 789 for regional ops, which is why it is configured similarly to what I expect the 78J will be like... small lie-flat J and no PE.
Of course once they have enough 78J in the fleet, they may opt to reconfigure 789 for long haul ops.
And I agree that Australia flights should see decent PE sales in theory - it is long enough and with possible connections to Europe if timed correctly. But BR hasn't really clarified its Australia strategy.