Mach tuck? Spin? What? You might as well speculate that the ap failed and it flew off into orbit.
Admittedly it is unlikely, but there have been multiple instances of ADIRU failures that have resulted in uncommanded and unexpected aircraft maneuvers. Malaysia had one in 2005 in a T7 as I recall. While these faults have supposedly been fixed, one never knows; these are devices that are highly complex and they are only as good as the programming that goes into them.
Almost all accidents involve multiple causes. An ADIRU fault resulting in an uncommanded maneuver plus an incorrect response to that maneuver could, at least in theory, explain an inflight breakup.
In any case, I readily admit that this is idle speculation. The aircraft will be found, the investigators will do their work based on facts and evidence and the cause identified and hopefully something will be learned that makes aviation safer going forward.