Many good points and thoughtful remarks in this thread. That said, It is well known that both natural and synthetic organic coatings can crack (natural resins like damar, shellac, gelatin, and more modern ones as well like PE, PVA, PVB etc. etc). Some coatings have been applied in ways that make them highly sensitive to microcracking, and/or delamination, but these and others have also been applied in ways that allow the artwork to be enjoyed for centuries. Environmentally induced mechanical stresses that lead to microcrack formation, crack propagation, and in extreme instances coating delamination was a huge part of the research I conducted with colleagues when I was at the Smithsonian institution. I was personally interested in low temperature storage of color photographs and films made on acetate and nitrocellulose base to save these works from thermally induced degradation which can occur at an alarming rate at normal room temperature. Low temperature storage and return to use/display environments forces a temp/humidity cycle and thus induces some stresses on the objects. Could the art tolerate the stress cycling better than the thermal degradation that would occur in steady room temperature storage? That was my concern, and to find a technically sound answer required a rigorous scientific approach. Similarly, my colleagues were interested in environmentally induced cracking of traditional paint and varnish coatings on canvas, wood, etc. Our research group thus tackled these environmental and material structure issues to better understand the role of low (i.e."flatlined") versus moderate versus wide temperature/humidity cycles within the Museum environment and how detrimental fluctuations were to the chemical and structural safety of paintings and photographs. As the research progressed we were able to successfully model the mechanical response of paintings and photographs to changes in temperature and humidity using modern engineering programs and finite element analysis, and we demonstrated that there is indeed an elastic regime where paintings and photographs can cycle indefinitely without being at risk. It was very controversial research at the time because it showed that very tight environmental controls being recommended at the time could be safely relaxed to the point where huge energy savings would accrue, ie., that perfect "flatlined" humidity and temperature offered no superior safety over environments that were allowed to swing between 35-60%RH. Today this research has been vindicated and indeed embraced under new "green energy" initiatives being advocated today in the museums and archives community. I mention all this to back up my confidence that not all inkjet coated media are going to fail so catastrophically as the IPI results would seem to suggest.
I guess it comes down to what risk of failure you're willing to accept. For general-edition prints, I have no problem printing them on coated papers - I particularly like Hahnemuhle Photo Rag Pearl and Silver Rag. They'll look great on display, but I have no expectation that they'll last more than fifty years of real display. For limited-edition prints and special works (e.g. for galleries or certain institutions), however, I'd prefer to eliminate as many things as possible which can fail - the institutions to which these are sold may have been in existence for hundreds of years, and these items are the sort that are likely to be passed down generation to generation, or belong to a collection.
The cited IPI article is a non peer-reviewed paper with an agenda, IMHO. The researchers deliberately selected just two undisclosed inkjet papers out of hundreds on the market, and they ran a primitive strain-to-break tensile test (there are much better ways to measure and the elastic/plastic deformation characteristics) where even the control samples "failed" at some vaguely measured value in order to demonstrate that inkjet coatings can crack. The conclusions based on just two non randomly selected samples
is somewhat pathetic, IMHO, but I will cut IPI some slack by reminding myself how IPI typically approaches its primary audience. IPI's audience is comprised of many librarians, archivists, and conservators who anxiously look upon inkjet media today as some new and mysterious medium they are now beginning to have to deal with in their professions. So, to show a picture of a cracked or delaminated inkjet print, whether by inducing a failure in the lab or finding a real-world example, is indeed informative to this group at a very simplistic level. What the research fails to do give us is a proper context for better understanding the extent of the problem in real world use. More research is needed and with a much better design-of-experiment methodology. I've still got access to my colleagues (they are now retired but still active) and the equipment needed to conduct this type of research. What I don't have is the funding, and grants are only given to non-profit institutions like IPI, so again, it comes down to a funding bottleneck for me to start this work. But I do think it's perhaps the most important initiative after light fastness research to undertake on modern media, and I am trying to think outside the box on ways to be able to accomplish this research.
I guess it depends on what conclusions you're trying to draw. Certainly, you can't draw any definitive conclusions about which coatings are better than others, exactly how they fail, or how long you should expect the coatings to last in real-world display. But the only conclusion I'm trying to reach in this case is, 'current inkjet receptive coatings can crack and fail and brittleness is increased by exposure to UV light and pollutants, whereas there is no layer on uncoated papers that can potentially fail' - and these preliminary tests illustrate it perfectly.
More tests are certainly needed, though, in order to find a solution.