A lot of microbiome research is leading to particular bacteria in or missing from the gut being correlated with various diseases like diabetes and obesity and almost all chronic diseases have a corresponding microbiome adjustment. We don't know yet know if there is a cause here or its just correlated but its a potential diagnostic that shows long before more serious symptoms and could potentially be used diagnostically one day. Or it might be these shifts are causal and we need to find a way to restore gut function that works well and reliably.
The fundamental idea is becoming mainstream in research with significant labs working on this for Long Covid, ME/CFS as well as EDS across the globe. Its not a fringe idea in research looking at long neglected diseases and the more they look the more they find evidence for it. Its not something the vast majority of doctors would have any knowledge on today, most would consider it ridiculous despite thousands of papers on this topic with growing evidence for the fundamental idea of ongoing infections causing increasing problems.