I've no idea what causes or perpetuates ME but I'm pretty certain there's a crucial clue hiding in the delay aspect of PEM.
I'm less enthusiastic about that approach. I think that the delay from physically-induced PEM is explained by the immune response to muscle usage (and damage): The immune cells have to detect the signals of damage, communicate that to other cells, then there's an orchestrated response, which in turn triggers a response from glial cells, after another delay. Cognitive exertion could trigger the same response from glial cells without several of those delay steps. My physically-induced PEM had a consistent 24 hr delay, while cognitively-induced had a shorter (<1 hr) and more variable delay, probably dependent on the magnitude of the exertion. I'm still impressed by type IV sensitivity responses: a precise and consistent delay of 48 hrs +/- maybe 5 minutes. What sort of timing mechanism is at work for that?
The other reason I'm not in favor of focusing on PEM is that I managed to cure my PEM, but I still have the other ME symptoms: lethargy, brainfog, aches, sleep problems and some other minor symptoms. So, curing PEM does
not cure ME; it's just one symptom. Figuring out the mechanism of PEM could possibly provide a clue to whatever dysfunction is triggering it, but I don't think it's likely to be so important of a clue that it will quickly solve ME.
I still favor the black-box approach: try a lot of different inputs, such as chemicals, and look for any reliable responses, positive or negative. If they stumble across a reliable beneficial factor, maybe some slight modifications might make it a useful treatment. I'm fine with a treatment that they can't explain why it works.
A factor could narrow down where to look; if it doesn't cross the BBB when swallowed, but does work sublingually, focus on the brain rather than the gut or muscles. If a chemical does have a reliable response, try to find cofactors, which can narrow down how it's doing whatever it's doing. If there's a consistent delay, that too helps narrow down how it's working. IF ME is caused by a slight change in some ratio of certain molecules, and limited to a small area of the brain (the ratio is blurred out only mm from the cells), then it's going to take a very very long time to find it by looking for differences between patients. My ME has responded (mostly negatively) to quite a few factors, and I expect that's common for PWME. I wouldn't be surprised if the typical PWME responded to at least a few dozen common chemicals (herbs&spices, etc). The problem is reliability and consistency. I respond badly to cinnamon, but others find that it helps. However, if they tested enough people, there might be some reliable common factors, which could be useful clues.