With regard to the possibilites of what did happen and what could have assisted in such Wild, I'd recommend re reading the earliest posts, both onsite/here and the 2 related threads at ww2...
Apart from than those few aeronautical/engineering/logical/flight and knowledge based assumptions and the statements of some witnesses, there isn't much left (if any) that'd believably end in such a result - all thats left is what mechanism(s) broke first which led to the trimmer acting so suddenly that one of its mounts failed, leading to the aerodynimc windblast of 480+ (more like 490+; as he was pushing Rare Bear hard & very very closely, which itself is uncharacteristical of Jimmy.) suddenly hitting a tiny lil' bit of tab at an angle and speed it never experienced before, and so peeling it away from the elevator leading to the pitchup & 1/2 barrel-rolling loop.
We all would love know 120% what happened to help prevent worse in the future, but as its a extremely 'unlimited' modified racer, running at high race speeds 480mph+ at roughly 80ft alt (above the terrain underneath), and the human brain has for the last 40,000+years been used to going roughly 4mph - not holding this against the racers & Jimmy; whom are used to such speeds, but more to those of us who aren't.
Anyhow, all we can adjectively do now, is await the collective experiences (hopefully) of those there will be filtered, checked, & pieced together by the NTSB Investigators in their (eventual) Accident Report along with any aero/engineering findings they are able discover.
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Edited slightly, as I realised I seemed to be adding the wrong 'inflections'. - I tend to write first, & redraft later...