I raised the point about time being an effect, similar to temperature, pressure, color and sound on a previous post and agree one of the overlooked properties of space is equilibrium, along with infinity, but I thought a paper you might be interested in, with reference to the issue of all frequencies traveling at the same speed;

2008CChristov_WaveMotion_45_154_EvolutionWavePackets.pdf

Argues that while single spectrum light will only redshift due to recession, multispectrum light "packets" redshift over distance, as the higher frequencies dissipate faster.

This goes to the current expanding universe cosmology and a possible alternative explanation for cosmic redshift. As such, it might be an observational test of this difference.

Of my various arguments aginst BBT is the proposition put forth that space itself expands, is illogical.

It was originally assumed to be an expansion in space, but as it became apparent cosmic redshift increases proportional to distance in all directions, making us appear to be at the center, the idea became that space itself must expand, because "spacetime!"

Which ignores the fact that if intergalactic light is being redshifted, it isn't constant to intergalactic space. Two metrics are being derived from the same light and the speed is still being treated as the denominator, or it would be a "tired light" theory.

So given we are at the center of our point of view, an optical effect would be the logical place to look. Likely one that compounds on itself, to explain the curve in the rate, currently assigned to "dark energy."