Expectations vs reactions
RetF4 thanks for your several well thought out posts. But your conclusion that early stall avoidance may require uncomfortable and never before experienced sensations (dirt, papers, coffee, and appendages rising) that will in many or most people inhibit proper actions appears to me to seamlessly morph into a prediction of lingering angst resulting from any exposures to sub G training "in any suitable" AC. You term these physical benefits as improved "tolerance", 'tolerance' suggesting an increased ability to withstand a discomfort. Perhaps my sub and negative G introduction and subsequent investigation was different, and that probably people in general will have widely varying reactions, but I think a distinction should be made between "tolerance" and "familiarity".
I may learn to become tolerant in the dentist's chair but I don't know if I will ever become as able to act with as much speed or finesse or total SA sitting there with the drill screaming if the chair also jumps off the floor, the building begins to sway, and the fire alarm goes off. "Familiar" however implies a reaction where a sensation has become so well known that the fear of it or angst about it has been surpassed. (However I don't suggest that training to familiarity in the dentistry illustration would ever reach a place of personal ease:-)
I realize I am drawing a fine distinction here, but I don't think it is negligible.
I know that if I had a choice between a pilot who I knew tolerated sub or neg G, and one who was entirely familiar with it, I would choose the latter. I also know that if I knew one airline for which zero awareness or minimal tolerance was the norm, and another where all aspects of piloting were encouraged to be explored for all anticipated flight regimes, I would also clearly choose the latter. It has come as something of a surprise to me to find that the airline industry has evolved to systemically include as much aviating slack as has been reported here.
High altitude stall events as under discussion now are rare, but I don't see that at as any reason to avoid comprehensive training covering anticipated flight regimes, especially when once a stall has been entered there is along with a lot of brand new potential circumstances, a relative dearth of Plan B's. Training today certainly includes other equally rare events that are thought to be essential. Acro aircraft and pilots looking for any excuse to bore odd shaped holes in the air are sprinkled everywhere around the globe everywhere and are cheap compared to dredging the occasional large aircraft. I'm not suggesting acro sequence training for everyone. All we are looking for here is a cheap effective erasure of angst. But like any piloting skill, such exposure demands currency.
Cloudcutter suggested that an intellectually (not physically) informed anticipation of a set of sensations will be sufficient. My experience taught me any never-before-experienced sub or negative G sensations, particularly combined with stress, is going to leave one less able to respond no matter the amount of intellectual preparation.