Georgina,
You've said the same thing for years, but never so well before. Congratulations.
One reason this essay is so cogent is that you focus on the 'objective world' and 'image reality', both of which exist as physically comprehensible phenomena, and you have not mentioned (except implicitly) the 'subjective world' (that we know interprets the images).
Your sequence of presentation is superb. Your explanation of 'current time' vs. 'present now' superb, and you make many sorely needed observations, such as:
"...the medium...must exist to account for observations...without having to resort to many worlds supernatural interpretations of reality or the belief that hypothetical constructs [wave functions] formed from mathematical equations without real counterpart in the object universe control the position and momentum of real particles, or that nothing is real."
You have laid it all out so clearly that I believe you may wish to look at the Maxwell-Einstein gravito-magnetic aspect of gravity [that I call 'the C-field'] --the gravitic *analog* of the magnetic B-field induced by moving charges-- as a physical field that can do duty as your 'unseen medium'. The C-field is induced locally by moving mass. It's 'wave like' existence accompanies every electron and photon with momentum and interacts with other mass/momentum in the neighborhood, including 'two slit' apparatus. It is a 'real' field, not a mathematical construct like the wave function, but it has the same mathematical description as the wave function. See figure and function at top of page 6 here.
I intended to just compliment your fine essay, but since you have 'set up' things so well I cannot resist trying to show how well the C-field fits your need for unobserved 'medium'. The existence of the C-field is not in argument, but its strength and significance is debatable.
You have, in essence, made the argument that [something like] the C-field is needed. I hope you will give serious consideration to the reality of a field that behaves as you say 'a medium' must.
You have also held up for closer examination such ideas as space-time, wave-functions, many worlds, and extra dimensions and found them lacking objective reality. That's a lot to accomplish in nine pages.
Edwin Eugene Klingman