I agree with most of your views here, except this. Passing out (not graying out) is uncommon. But still happens. This is usually a loss of consciousness caused by g-force. Over all of its Florida rides, Disney sees around 20 riders who are reported unconscious (and usually sent to the hospital) per year. I don't know how many of these are coasters or thrill rides--heat also plays a factor. In terms of Universal, the restraint system is supposed to protect riders who have passed out in a way they are safe inside their seats as the coaster finishes its circuit. This should be true for ADA riders and riders who are amputees (within the defined specs for both categories). It looks like this didn't happen here. If there was some underlying health factor that contributed to his death, we would've heard about it with the initial medical report. And it wasn't in there.
That's kinda the whole point of what I said though. It's supposed to protect riders and that includes riders who have specific ADA needs and specific kinds of amputations. That is what it is designed for. It was cleared and approved by all parties involved because it met these standards. The fact that in this specific instance the rider was not protected suggests that the rider was not fit to ride the attraction and fell outside of the defined rules for rideability, but in such a way that was not easily visible or predictable to the rider or the team members involved.
There are various reasons why someone may be denied the ability to ride an attraction. One of these reasons is if they have a disability or something else with their body that would make it so that the ride's safety parameters would not be as effective on them as it would be another rider.
My point is that I believe, given the information we have as of now, this was probably the case with him and that he should never have been given permission to ride it in the first place, but permission was granted because the parties involved did not have the extent of the information required to make a completely informed decision, and that likely includes the rider himself. He was alright through his first rides because he was conscious and able to exert some control over his body, but when unconscious, that seems to have turned out to not be the case.
Yes, rides are designed with people potentially losing consciousness in mind. They are not however designed for people who do not meet the attraction's rideability criteria in mind. That is why this criteria exists.
Just because someone can board an attraction does not mean they meet the criteria for being able to ride it. Disabilities are complex, and the dangers they present when it comes to attractions may not always be visible. Case in point my father who was allowed to board an attraction at Six Flags because he was able to board and upon visual inspection looked as if he met the criteria. In reality, he did not, and he knew that and was dishonest with the employees about it. Thankfully, nothing catastrophic happened, but he did indeed have some issues with his restraint fitting him properly through the ride.
That is not at all to suggest this guest was dishonest about his disability, and it is also not to suggest that the team members were not thorough in making sure he fit the criteria as they knew them to be.
It is to suggest however that the nature of his disability meant that in this specific scenario, his loss of consciousness could've become a danger that would not have been present if someone without that disability had lost consciousness on the ride. He had a spinal disability. It is very possible that he was able to power through said injury through his own will and determination, but when he was not conscious and able to control his body, his body could not do the same thing on it's own. That is something that is difficult to pre-plan for, but could also have been something that could've come up in the screenings that get done for disability access in the parks if the right questions get asked.
I don't think anything about this is a result of purposeful negligence or ill intent. I think it was an unfortunate storm of different factors coming together to make this ultra specific scenario happen. I don't think it was an issue with the ride whatsoever, but rather someone who in normal condition could handle it but in an abnormal condition was unable to.
There will indeed likely be changes to Universal's operations overall and Stardust Racer's operations specifically. But I think these changes will be in terms of disability access to the attractions, rather than any sort of modification to the attraction itself.