Aren't all theories essentially metaphysical? like... the theory that the scientific method produces better results than, say, prayer, or that Occam's razor is better than extremely convoluted conspiracy theoires?

I think you're onto a loser here, since all metaphysical theory is equally implausible merely by being metaphysical. That's basically because all metaphysical theory is absolute, and cannot be formulated in ways that are incrementally assessable in experience. There are thus no possible non-dogmatic criteria for differentiating any one metaphysical theory as preferable to another.

https://www.youtube.com/watch?v=1D7zaW3Mfbs&index=17&list=PLn5pVvpmka7qNJzvVDmkdmrjs6uprcZGV

Application of mathematics and game-theory to metaphysics, Pythagoras and Iamblichus - can't wait to read the paper when you finish this work.  Not sure if you can apply a version of Bayesian modeling or string theory to the metaphysics of Pythagoras and Iamblichus, but the attempt would be fascinating.  Since the writings of Pythagoras influenced string theory, and he determined the most pleasant musical intervals, this might apply to his metaphysics too? 

At one time, quantum physics was thought to be an un-measurable metaphysical construct existing solely in the realm of physics and mathematics.  Then, technology caught up and we now know more than we did 30, 50, or 75 years ago.  

Unless you need to mathematically define "the measures of implausibility" for the purposes of your model, why not test the hoop theory using a "multiple best fit" analysis (of course, multiplicity would be utterly out of control in the first few cycles) and see what the model generates?  In the end, you may end up with a string that vibrates at 440 cycles (the standard key of A).  Thanks for such a stimulating question.

Many thanks for these answers -- all 3 helpful, interesting and thought-provoking!

I posted my question (re criteria) partly because I find both Iamblichus' system and Gillian's Hoop deeply  and about equally implausible -- but for rather different reasons. Each appears to me to be something of a jeu d'esprit reflecting contemporary (to its creator) intellectual fashions rather than convincingly searching for possible metaphysical "reality ". Someone must have gone into this in detail...

Thanks again!

Jim

If you believe that you can find some "metaphysical" notions implausible, it seems that you must have some sense of what is plausible. So perhaps you need to start by trying to state what are implausible features. You will have to address, as well, the skeptical position: why believe that your sense of plausibility is itself plausible?