No, but I’m aware of the general gist of the safety arguments people make as a justification for the tagging scheme. I don’t really think it’s an issue outside of rock paths though. Sure, maybe you could trip over a log with long grass if you didn’t see it, but that can easily be solved by mapping the log and the existence of potential obstacles doesn’t have anything to do with how visible the trail is anyway. For instance a trail can be tagged as trail_visibility=excellent and still step in a goffer hole, break their ankle, and need to be air lifted to a hospital after spending multiple days vainly trying to limp back to civilization while they mumble about how the trail being tagged as trail_visibility=excellent didn’t do anything 
I’ve actually been in similar situations BTW. In one case it was a pretty visible trail that abruptly ended in a pot grow that unfortunately wasn’t mapped. Also, a dog ran out of the woods and attacked me once (well, actually it happened twice, but whatever). At least the trail visibility was excellent in both cases though. So…To repeat what I said early, I think it’s a solution to a non-exiting problem. There’s zero evidence that anyone’s life has been saved or made safer by tagging paths with trail_visibility. And no a clickbait article about “concerns” over crowdsourced maps isn’t evidence. Although I did say I thought it was fine to use on rocky paths since there’s clearly a use case for it. I just don’t think there is for any other surface.
What surface a trail is might be one of, if not the main, way a hiker goes about determining how difficult the path will be. For instance walking across an icy, snow covered dirt path in the dead of winter is a completely different animal then taking a stroll down a gravel one in the middle of summer. Even if you confine it just to rocky paths in the summer the type of rock your walking on can make all the difference. Walking on lava rock is completely different then walking on shale or sediment. Heck, have you ever heard of quick sand? How exactly would the trail_visibility tag help at all in that case?
I don’t mind it either. But again, we are here to discuss and solve a specific problem. Not to just wax poetic about how everyone can tag things how they want or map whatever they want. There’s nothing wrong with that, but it’s not the topic of the discussion. Improving the trail_visiblity tag is. Anyway, I don’t disagree that paths can be dangerous or that those dangers can partially be mitigated through mapping them somehow. I just think that it should be done by mapping the actual hazards. Not tagging a a path with some completely ambiguous tag that doesn’t actually say anything about what the actual hazard is or where its located along the trail. Like I said, if there’s a log in the middle of the path, cool. Map it. There’s no reason to overcomplicate that with something like trail_visibility though. If anything it just makes things more dangerous because it disincentivizes mapping the actual hazards.