Our understanding of the gut microbiome is really primitive, we really don't know what a great one looks like. More problematic is that quite a lot of the bacteria that are critical die in the presence of oxygen and are thus very hard to collect and reintroduce. So far no one has made a mechanism to keep them alive and reintroduce them into other people. I would not be quick to rush to a fake biome just yet, it will almost certainly be lacking in a whole range of areas.
That’s the problem of unculturable species that pervades microbiology and anything related like agriculture. We have no idea what percentage of bacteria species can even survive long enough to be studied in the lab let alone industrialized. Even if someone manages to grow them accidentally, we’d never know it because if they don’t absorb any of the known stains, it’ll just look like agar on a plate under a microscope.
Last I checked the “state of the art” was to use a freaking electron microscope and hope that the plating process didn’t destroy the sample.
