Peter,
My one-way definition of the speed of light in empty space is apparently too simple and irrefutable as to be accepted by you. What is the obstacle?
Everybody is used to refer speed to something. You mentioned "the rest frame of the fermions" and "the sol rest frame". Persson's essay (A Tragedy in Physics) mentions "boundary conditions that are relevant in relation to the wave motion".
In contrast, I agree with Einstein on that there is no naturally preferred point of reference, no rest frame in space. Because my definition is restricted to empty space, it does perhaps not collide with your focus on reemission by fermions. I wonder if I am the first one who claims that the far field of light waves in empty space simply propagate with no direct reference to a frame of emitter, reemitter, medium, or receiver. Only the distance matters, not an arbitrarily chosen point of reference. Did nobody else already distinguish between empty space as a medium as Maxwell imagined it and empty space as mere mutual distances?
Incidentally, what is your opinion concerning the conflict between limitless growth of world population and protection of nature, etc.? I guess, I understand the voters for Brexit and Trump to some extent. Germany's future president often says the world is out of joint. I see a necessity for correcting ethics.
Eckard