I don't think FADEC failure is likely, as there appears to have been a possible common-mode failure affecting the ability of BOTH engines to respond to throttle demands, and the FADECs on the two engines are functionally, electrically and physically independent.
Although the design goal would be for the all engines to be functionally, electrically and physically independent, the QF2/7JAN08 incident (VH-OJM / MSN 25245) is being unofficially attributed to a common mode failure affecting the power feeds from all
4 engines
and the APU (this was a 744).
And given the history of power supply disruption on B777 (see my previous post, referencing AAIB/SB/2007/2), I'd say that FADEC issues can neither be ruled in nor ruled out at this juncture.