Degrading light sounds like an interesting idea to me, you could call it the “cosmological damper” if you will.
Thought experiment: imagine you have light particles in a perfectly circular orbit around a black hole. Does the light ever fall into the black hole or does it orbit for eternity?
There a whole set of theories, called "Tired light" theories, which tries to explain Cosmological Red Shift by degradation of photons with time. Buy they require whole set of different cosmological principles: a medium for light propagation is required to dump lost energy into, no Big Bang. But even with a tired light theory, galaxies are accelerating toward attractors, see https://arxiv.org/pdf/1702.02483v1.pdfhttps://www.youtube.com/watch?v=NpV0GQo3P0c
Many black hole solutions of the Einstein Field Equations of General Relativity admit a photon sphere or equivalent(s) where light can orbit the black hole, but not usually stably, and in physically reasonable black hole solutions there is no stable circular orbit for light at all, so no eternal orbit. (The orbit can be quite long on human scales though, before the light eventually leaves the area around the black hole, or spirals into the black hole).
> Hawking radiation would interfere with the eternal orbit
For tractability Hawking radiation tends to be studied using a non-interacting scalar field (often massless), rather than the fields of the Standard Model (which are very much interacting, and have a variety of masses).
Hawking started that in his "Black hole explosions?" (1974) which (if you're not allergic to sci-hub) you can read at <https://sci-hub.se/https://www.nature.com/articles/248030a0>: "consider (for simplicity) a massless Hermitean scalar field \phi which obeys the covariant wave equation ... in an asymptotically flat space time containing a star which collapses to produce a black hole.". In the short paper, he's very much not considering photons or pions, and really doesn't need to in order to make his point.
The thermal spectrum of a real black hole will be in all the Standard Model fields, and except very late in the eventual evaporation will be dominated by very low energy photons originating at a fair distance outside the event horizon.
What do you mean by "eternal orbit"?
Real black holes do not extend to the infinite past. If a black hole ultimately Hawking-evaporates, in finite time there's nothing left to orbit. Late in the evaporation, there will also be a lot of very high energy gamma rays and heavier particles excited in their respective quantum fields of the Standard Model. These will all tend to participate in high-energy multi-particle interactions rather more complicatedly than the end result of Hawking's 1974 description.
