Obviously, it's too early for a definitive cause to be determined....
That said, if there was no failure of the aircraft, the pilot (Hill) will own it. It's that simple.
In this case, I'd give odds at 100 to 1 that there was no aircraft failure.
Air show professionals have stated privately that the maneuver was started at or below the air show minimum altitude (AGL) for any aerobatics, and the apex of the maneuver was far too low to have even a shred of margin. One suggested that seeing his altitude was insufficient, he should have rolled out at the top of the loop. Unlike Leslie Hatcher, these gents will keep their opinions among themselves and await the accident report. It wouldn't be the first time an air show pilot G locked himself when falling below minimums.
Of course, we'll never know what was going through Hill's mind until they can talk with him, and that will probably be a while before that happens.