In my experience, what happens instead is that the exact process you describe occurs, and results in disagreement and competing standards. Which is pretty much what we have now. As I said, I like the concept, but I don't see how it ever ends up with a single authority, even within a given group of arts.
Let's start with a simpler question: what would be certified? That, even, would likely be an area of contention. Does it certify that the instructor has trained for the number of years they claim (with whom, at what regularity, etc.)? Does it certify that they're approved to teach (approved by whom, to teach what, to what level, etc.)? Does it certify that they are passing along something that accurately represents that art (as designated by whom)?