Reddit mentions of Gut: The Inside Story of Our Body's Most Underrated Organ

Yes it seems the research is ongoing. I read a book called Gut that went into some of the research at a high level. The author seemed to lean toward the idea that while most of the microbs in active culture are probably killed, if even a few get though they can multiply and the biome can change so rapidly in general that there might be some additional benefit to probiotics (actual living organisms) over prebiotics (nutrients for your biome but not active cultures). Just watch for added sugars in your yogurt.