Re: So we've gone from six to five
"I'd really hate for our measurement standards to end up as one big Catch 22 or chicken/egg paradox"
What, you mean like being dependent on something as parochial as the rotation period of a particular planet in a binary planet/satellite pair(*), in a particularly short window of a period of their 7-8 billion year lifespan?
Or the circumference of that particular planet?
(*) Earth/moon are frequently described as a binary due to the size of the satellite having an easily observable effect on the barycenter of the pair (it's about 75% of the way towards the surface from the earth's core). It's not a classic binary inasmuch as the barycenter is still below the surface of the earth but it does mean there's a hell of a wobble in there and it would have been a true binary originally)