which surely makes it extremely difficult to prove recklessness and almost as difficult to prove negligence, especially in a high stress situation such as an airshow?
Random thoughts on my part, not incident specific...
I would not view an airshow performance as being "high stress", if properly planned and executed, I would think it more precision demanding. If a public or otherwise demanding aircraft operation is "high stress" for a pilot, perhaps that pilot should either not be flying it, or should be doing so with a greater "box" size for safety. When I have displayed aircraft, I have done so with precision, in the "box" I had planned, with no particular stress at all - just fly the plan. Now if something goes bang quit, the stress level goes way up, but there should still be a plan for that, so there's no guessing, just executing a new plan on short notice.
If an airshow box for display is appropriate to the plane, pilot and environment, I think the pilot should fly the box without difficulty nor stress. If we all agree that the box, the plane and the pilot were suitable, the aircraft remains airworthy, exiting the box unplanned should trigger the need for an explanation. If exiting the box in the wrong way (caused harm), I can see that being an indicator of recklessness or negligence - either in flying the box, or planning and agreeing to fly in it.
We pilots have a public image to maintain - not the Ace McCool white scarf thing, but the deliberate, planned safe execution of any flight, with planned room for a minor unplanned event, and an escape path for a big event. These sad events should serve as a reminder to us that we always must do that well - to protect the public from the effects of what we do....