... whereas there is no layer on uncoated papers that can potentially fail' - and these preliminary tests illustrate it perfectly.
true, but that doesn't mean uncoated papers don't embrittle upon exposure to light, heat, humidity, etc, and uncoated papers can discolor uniformly or with uneven spot patterns (foxing), tear or disintegrate, and are often very susceptible to mould and mildew owing to the traditional sizings used like starch or gelatin. Moreover, the possible risk of a coating failure is often outweighed by other durability factors imparted by a coating to the paper substrate. For example, I've seen many examples of foxing on old prints made on uncoated paper... Nasty Brown spots randomly showing in an image due to localized degradation within the sized paper which are typically more visually disconcerting than a few minor cracks in an otherwise unaffected coating. In contrast, I've never seen foxing of any kind on baryta coated papers. A durable coating often hides sins of deterioration going on in the paper base or on the mount board of vintage photographs.
Like others, I have a great personal interest in improved inkjet printing on uncoated papers, but I'm not ready to abandon coated papers. They serve a need, and they can be very durable and long lasting if one chooses wisely. Your 50 year expectation for longevity of all coated papers is unnecessarily pessimistic. Btw, HN Photo Rag Pearl is a personal favorite of mine as well. The coatings on Photo Rag Pearl and Photo Rag Satin are quite unique, less prone to cracking than other luster and satin inkjet media, and both are very forgiving when spraying with a protective spray like Premier Print Shield, HN Protective Spray, etc. They tolerate two or three coats with little alteration to the surface texture and luster of the inkjet receptor coating, yet differential gloss and bronzing are eliminated. IMHO, other vendors don't have comparable offerings to these two papers.