The whole concept of biomarkers is very confused. Recently (2018) there was an investigation that found various agencies use different definitions of biomarkers. See for example
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5813875/
Often when biomarker is cited, especially by doctors, it means diagnostic biomarker. There are a lot of other kinds.
At its simplest level, not often used this way, a biomarker is simply a measurable biological anomaly. ME has more than 2500 of those, and I stopped counting years ago. This is how I think of biomarkers myself, and will use "diagnostic biomarker" or some other designation to mean one of the alternative definitions. To me a biomarker is just a biologically significant marker.
Diagnostic biomarkers either need to be unique, or there must be an easy way to differentiate between disease states that share a biomarker. ME shares biomarkers with at least sepsis, severe burns, and African Sleeping Sickness. While it is probably not hard to rapidly differentiate between these four, it does raise the question as to how reliable these markers might be because they might exist in many other diseases and this has just not been discovered yet. If a biomarker is found in many diseases it is much less useful diagnostically.
Take the nanoneedle. It is highly likely in my view that it will find abnormalities in a range of diseases, including mitochondrial disorders. However it might be used in other ways than diagnostically.
Outcome biomarkers are very useful. The nanoneedle might be used as such. If a treatment improves results measured by the nanoneedle it might indicate the treatment helps . . . but there are potential confounds that might invalidate that. Its an indicator, not proof. It might tell us what is interesting so we can do further studies.
We know so very much about what is going wrong in ME right now, but we don't have a proven core causative mechanism. I suspect the comment on a biomarker was on such a postulated finding. Many groups may have found one, including OMF, or they might not have. In either case there is a long process to go through to test such a marker. There is no substitute for doing the science, which takes time and resources. All our groups lack sufficient resources.
In ME we might be able to find biomarkers that show severity or outcome, or even subgroups. There are many possibilities.
The mere knowledge of a biomarker does not, in my view, necessarily lead to accurate diagnosis or effective treatment or cure. Its a step along the way.
If ME is more than one disease, or some kind of spectrum disorder, we might wind up with many more than one diagnostic biomarkers.
The key core mechanisms might not be useful diagnostically, and so the tests wont be for them, but they might still be useful for considering targeted interventions.