I think its fairly obvious what the long term objective is - convert everything into salary and get rid of the concept of overtime completely. Thats why the twelve hour shift has to go.
In a heavy maintenance environment this may be a trivial change, but in a line maintenance environment, it means that the costs and risks associated with the uncertainty that is part of the job (ie: Aircraft delayed arriving for maintenance, trouble shooting etc.) is born entirely by the employees.
To put it another way, the company no longer bears the cost of uncertainty or its own poor scheduling as in: "No matter when the aircraft arrives, no matter what the problem, the trained monkeys will fix it before they go home, in return for their standard weekly ration of peanuts".
There is at least one academic theory of management that says managers exist to insulate workers from the day to day uncertainty of business and provide continuity and an orderly business process. It appears to me that Qantas management is basicaly trying to weasel out of the responsibility of managing and scheduling its own maintenance in a cost effective manner - at the expense of its employees.
This is not a win/win situation and is therefore bad (and stupid) management practice.