Well, I have celiac disease, and I wasn't diagnosed until around the time I turned 40, and I was only symptomatic, or at least what I thought was symptomatic for the prior 9 months or so to that.
Now, that aside, I can look back over my life ans see all kinds of signs:
dental cavities since I was a kid - malabsorption
night blindness while driving since I started driving at 16 - malabsorption
a period of time where I could eat ANYTHING and not gain weight - malabsorption
brain fog and a bunch of other things - malabsorption
Celiac disease is not easy to diagnose, and may be causing problems in a much larger group of people than those who have the most obvious and debilitating symptoms.
The way I look at it with the all or nothing argument can be distilled down to something like this:
Is there any such thing as a "little" bee sting?
If a "little" bit is ok, then why do medications as tiny as Valium, Zoloft, Aspirin, Tylenol, Sudafed and everything else have any effect on us when those pills are so tiny compared to our bodies?
In other words, shouldn't we have to gulp a plateful of medications in order to get them to work?
Or is a little bit just enough to cause changes - some noticeable, and others not so noticeable?
The "all or nothing" argument is as good as the metric it's based upon, and how much we can definitively say is good or bad. That's confusing at this point, and not well sorted out in quality research, but as the OP stated in the original question, it's looking more and more like gluten isn't any good for anybody, not just people like me who went through the very classic and extreme problems of celiac disease, and I now have a whole network of friends who have what they now call "gluten sensitivity" because they dropped gluten and a lot of problems like symptoms of MS, neuropathy and lots of other ailments that nothing else helped.
In short, maybe it's all bunk, or maybe it will all creep up on you in your 30s, 40s or 50s. Or not at all. It's a crap shoot, but the evidence is stacking up against it.