I see no reason for the Australian government to allow CX to serve those domestic segments. Sure, it would be good for CX, but codesharing wouldn't really benefit Qantas or Australia.
Those segments only exist to get passengers to/from Hong Kong, and it would be sort of silly if a situation came up as 'sorry we can't fly you HKG-BNE because the BNE-CNS segment is sold out'.
The situation can be solved by increasing CX156/7 to a daily basis as a compensation, and resume the use of A340-300 to these flights. (even B777-300ER in the future as CX has bought 14 more of the 77W)
Also, the codesharing between CX and QF can help QF to strengthen its domestic networks.