Would the fatiging illnesses be the best ones to piggyback on? Not sure what fatguing illnesses you mean and if ME and CFS would have enough in common to give meaningful results.
A while back I was at a talk given by a HIV/AIDS doc who spoke about new research into the gut of PWAIDS. They were looking at the idea of a leaky gut. Maybe these would be better to piggyback on to?
Also auto-immune diseases and drugs used to treat them? If there was a cohort of PWME and CFS then maybe we would find useful drugs to treat us as well.