Does it really matter whether a pack qualifies as "frameless" or not? Why not simply take a group of backpacks above a certain volume (not summit packs, etc) and below a certain weight and compare them to one another? If a frameless pack can carry 15lbs. while still being comfortable, then it's advantage will show in the results. If a framed pack carries much more weight with mere ounces of penalty, that will show up as well. In fact, graphing packs with a weight/volume/comfort ratio might be an interesting comparison.
Instead of testing "frameless packs for ultralight backpacking" as one category, just test "packs for ultralight backpacking" and do the same for "lightweight", etc. making sure the categories meet or slightly overlap. Fewer packs would "fall through the cracks" in that case and readers would still be able to select frameless or framed packs based on their own needs. The upside would be that the reader would be better able to evaluate the merits between totally frameless, removable frame, and framed packs of certain weight and volume classes. I doubt backpackers care much whether their pack has a frame or not, but they care a great deal about whether it's comfortable in their required weight range.
I recognize that this and the other SOTMR's represent huge amounts of work, but I've noticed that articles often experience discoveries during their creation that don't get fully incorporated into their earlier work. It's a lot of time and effort, I know, but after finding that folded CCF pads can be better, at least in some situations, wouldn't it be extremely useful to the reader to see that option in the previous graphs? And after deciding that inflatable pads do better as cylinders probably because they are more inflated and "stiffened", why not load the pack with the deflated pad folded and then inflate the pad to provide a similar comparison? It's rather obvious that the pad will provide more support when inflated, so why compare apples to oranges?
My two cents. Forgive my oversight if I'm missing something important. My criticisms and suggestions are not meant to belittle the impressiveness of this excellent series of articles. The authors' hard work is appreciated.