I answered the poll with '6-10 years'. This is probably slightly too optimistic, but I think there are a number of reasons for optimism.
As numerous people have pointed out in this thread, there's every indication that ME/CFS is a reversible, temporary state, not the result of permanent damage to the human organism. Between a lack of evidence of irreversible damage and the cases of 'overnight remission' (few and far between though they may be), I think that when ME/CFS is fully understood, there will truly be a cure, not merely a treatment. Whether the medical community reaches this understanding all at once or by degrees over decades remains to be seen.
However, we're already seeing some promising research, such as that regarding the metabolic trap theory, as well as HPA-axis dysfunction. For the latter, in fact, there's already a highly auspicious study for for the corticotropin drug CT38, which is a CRFR2 agonist that is believed to modulate the balance of the HPA axis.
Here's a good write up of the study's results. Again, it's unknown at this point whether CRFR2 is a key target in fully reversing the effects of ME/CFS, or if its limited to improving symptoms to a degree. But the 'sustained symptom improvement' seen in the study makes me very hopeful that if this compound gets through clinical trials it will end up being a big step for ME/CFS treatment.
In my mind, the biggest factor extending the time it will take to cure ME/CFS is simply lack of funding, or even more broadly, the failure to function of the medical research industry. As we all know, this disease is massively underfunded (that any progress at all has been made by this point is kind of a miracle). But also, there's no guarantee that
any medical research will continue, such as in the event of a third world war, or some global natural disaster perhaps relating to climate change. Regardless of your political leanings, I'm sure we can all agree that recent years have shown us that the robustness of our political institutions has been somewhat overstated.