Philip,
You have an amazing ability to "defuse" situations. Ideas that I tend to reject rather strongly when described by others seem much more reasonable when you discuss them. That is a real talent, in my opinion. I also like that, when discussing some of the farther out ideas you note that "we should not get carried away by thinking they are less speculative or more testable than they really are."
You have a most impressive grasp of the modern range of math and physics, and seem very comfortable moving over this range. Thank you for doing so in your excellent essay.
Your metaphor of chess playing aliens is a very clever way of contrasting 'invent' versus 'discover' math. And you seem to have split the baby when you caution not to worry about 'exist' [Tegmark's MUH] and then describe the 'ontology' in the next paragraph. You certainly have an impressive graphical representation of a metaphorical chart of mathematical ontology. It is quite a universe, isn't it?
I also appreciated your discussion of symmetry, generally conceived as the key principle that determines laws of physics. As I doubt this, I was happy to learn that "there is a growing movement... that thinks symmetry is not so fundamental." I tend to agree with you that "the fundamental principle that determines the laws of physics is universality, not symmetry." I have significant problems with the Holographic Principle, or more specifically with the "black hole information loss puzzle", but your analysis in terms of symmetry in terms of one degree of symmetry for every field variable is interesting.
If I understand you correctly I agree that "the structure that emerges from universality is also a mathematical structure in its own right." And that it is self-referential and recursive. And I need to reflect more on your idea of recursively iterating quantization. Finally you note that Tegmark's mathematical universe hypothesis tells us that all logical possibilities are equal. This seems to imply that there is more than one completely self consistent logical possibility [for the universe]. I doubt this.
In other words, as we've come to expect from you, a first-class essay! I invite you to read and comment on my essay.
Finally, having last year posted three papers on viXra, I wish to join many others in thanking you for creating that system.
My best regards,
Edwin Eugene Klingman