It may not be the ADIRU that failed
The ATSB report of VH-QPA, 7 oct 2008 describes the intermittent failure of ADIRU 1 during cruise, leading to sudden elevator movement of 10 degs, initiating a pitch down of 8 degs.
Could there be similarities, purely speculative, a possible impact by EMI because of earlier incidents in approx the same geographic area, near Learmonth, which lead the investigators to consider electromagnetic interference, so now coming back to this accident, heavy thunderstorms, nearby lightning, or even lightning strike. All components should comply with RTCA DO160-D, but if e.g. the ADIRU itself or interfacing wiring doesn't, there's a possibility for inadvertent flight control movement.
And further; there seems to be lack of comparison-check between the 3 different ADIRU's for the flightcontrol systems, FCPC's to base its decisions on. And last ; an ADIRU to cause an elevator deflection during cruise almost beyond the airplane's design limits , I wonder how most more elev deflection the airplane could sustain and where is the PRIM's protection against that.
rgds Peter