Dear Israel,
I truly enjoyed your essay. You have exposed with exceptional clarity some of the flaws in reasoning that led to abandonment of the preferred system of reference hypothesis.
I completely agree with you that the constancy of the speed of light is not experimentally founded. If a preferred system of reference existed, then any effect on the speed of light attributable to the motion of a two way measuring apparatus relative to the PSR must cancel out. What a two way measurement gets is the average relative speed of light, not the actual speed of light.
But there is, I believe experimental evidence of the existence of a preferred system of reference. Though the measurements of superluminal neutrinos claimed last year by the OPERA group proved to have been flawed due to systematic errors, it provided an opportunity to detect the motion of the Earth against the preferred frame of reference, hence to prove its existence. An unbiased look at the data used by the ICARUS group to refute the earlier claim of the OPERA group shows variations in the speeds of seven neutrinos of than 18 nanosecond below and above the time of arrival of the speed of light. The measurements, which here were one way, were then averaged out to the speed of light (and thus replicated mathematically the error from two way measurements). But, if a preferred system of reference exist, then the larger variations may be attributable to the absolute motion of the measuring apparatus against the PSR. Of course, this may imply, as I believe, that the speed of neutrinos, like that of photons, is independent of its energy and is equal to c.
That said, I am convinced that the constancy of the speed of light is not incompatible with the existence of a preferred system of reference. That is, if space is discrete and emergent, as I describe in my essay, then the constancy of the speed of light becomes a direct consequence of the structure of space itself. This implies, that any apparatus located on Earth provides measurements of the relative speed of light (or any other particle) between source and target and not the absolute speed of light (or particles).
I am convinced that non-biased analysis of the data of neutrino speed measurements will be found to be consistent with the existence of a preferred system of reference.
Thank you for offering such a stimulating essay.