Firstly independence. To be truely effective the system needs to be independent and not seen to leverage anyone's vested interest.
May I suggest rather that the unions "leading" this initiative, you take the initiative by "strongly supporting" an independent entity, like Aviation/Aerospace Australia, Australian Association of Aviation and Aerospace Industries, or Flight Safety Foundation... it would also be worth having a yarn to Chris Manning with regards to the The Australian Aviation Associations Forum (anything you want to achieve will be difficult if you don't get the RAAA on side early), and even BASI.
Apologies but I have to disagree here. We have independent bodies already. CASA and the ATSB. I think they are both pretty useless and I suspect one airline in this country would do all things possible to pamper any new independent body created. I would not waste my time, efforts and ideas by placing them in the hands of another useless group.
Please also remember this is not a reporting body that also does the investigation. We just report to those people who do the investigation to keep workers names free from their eyes. We would also be able to pressure them subtely and then openly for major problems they don't address. I think the strength of this idea is that it isn't independent.