For reference I've been playing VR since my early 20s (now early 30s) and never once experienced motion sickness. I have tried every style of game/locomotion, both well polished and incredibly janky, and have had 6hr+ sessions without interruption.
I'm pretty interested in this and would like to participate in a study as well if given the opportunity. I think one of the potential causes and solutions is it being a self-fulfilling prophecy that may be overcome with self-efficacy as described here [1] for seasickness. My only evidence is that I never knew motion sickness was a possibility when I first tried VR, and my friends with the worst motion sickness were worried about it before they even tried VR, even if they never get seasick or carsick.
From the article and other comments, they also mention figure skating which I never thought of before, and I play ice hockey which is likely similar enough.
[1] https://psycnet.apa.org/doiLanding?doi=10.1037%2F0021-9010.8...
VR is fun despite some discomfort, much like other experiences like roller coasters. I'd volunteer to participate in such a study because I'd like to do more VR than my body can naturally tolerate.
> Will people who condition themselves too well to tolerate VR entertainment also break their vestibular system
Definitely worth studying! From the few I've heard adapt, no, it doesn't make them significantly more likely to have balance problems.