I'm afraid I think the long term coevolution of gut biomes ship sailed around the time we started indiscriminately slaughtering those gut biomes with antibiotics. (not to mention importing large numbers of unfamiliar alternatives through changes in food systems, and at least in some cases raising kids in crazy-sterile environments). So I tend to agree with you that this doesn't seem like a good thing to rush into, but it's interesting as a possible form of repair.