The prokaryotes are already split into two domains, so there's no way they will be called subspecies of a single species. Note that all the millions of eukaryo

The prokaryotes are already split into two domains, so there's no way they will be called subspecies of a single species. Note that all the millions of eukaryotes fit into one domain. The domain is a much higher level than species. It's Domain, Kingdom, Phylum, Class, Order, Family, Genus, Species. See https://en.wikipedia.org/wiki/Bacterial_taxonomy https://en.wikipedia.org/wiki/Bacterial_taxonomy . Thus, it's hugely more likely that the intermediate classification terms will be used, rather than group everything a subspecies of a small number of species. Even if there are billions of prokaryotic species.