The second part is that right now it is somewhat unclear what is actually microbiome related problems. Clearly, associations to all kinds of diseases and conditions have been made, but the casuality and dynamics of the interaction with the immune system and host factors is not well-defined for now. It seems obvious that diseases in which we can intervene with a fecal transplant and improve an outcome are microbiome-related, but there isn't actually that many solid cases for this. C.diff infection is well-established. A recent RCT looks really promising for insulin resistance (i saw the senior author talk about it at a conference and i was certainly convinced), but naggingly insulin resistance wasn't actually the registrered primary outcome of the trial
http://www.stephanguyenet.com/microbiota-and-obesity-is-it-a...