well, after 27 yrs of searching, its rather odd i had never come upon this before...but recently i found several papers stating that norovirus, EBV, and some other viruses, have the ability to damage the neuromodulatory cells in the gut. This results in gastroparesis and voila. You have dysbiosis, inflammation etcYes, the research is thin on the ground. Ther is a reasonably large trial of FMT for ME currently in progress in the UK but suspended because of COVID. If this trial proceeds after the epidemic then it would contribute more peer-reviewed literature to the subject.
Whilst you describe this as a wild goose chase all I can conclude is that I was very sick and now I am not. Even I don't really know what to make of that.
It seems that the mechanism will revolve around the role of glial cells in the branch of the vagus nerve which connects to the bowel. Exactly if or how such a mechanism works is still to be elucidated but the "Vagus Nerve Hypothesis" by van Elzakker is instructive.
Fecal transplants are eventually going to cure every autoimmune disease, once they find out more about the microorganisms. There are probably hundreds of trillions of unknown ones so... lol might take some time. Look up all the case studies of people getting FMT for C diff and then going into remission from long standing MS, depression, bipolar, even epilepsy.Wild goose chase here. Research listed on the site is from 1995-2012. If there was anything to it then it would be more widely known. I can't even fathom a mechanism for fecal transplants affecting ME.