If the property of inertial mass were to decrease over time so that the intrinsic "rest energy of matter" were to also decrease over time, then electrons would slowly be drawn down into a more intense electrostatic field. This way photons produced in the past would have less energy imparted to them when they are emitted (or absorbed), than a photon produced in the present. Our present photons would be comparatively "bluer" resulting in a Cosmological Red shift.
Why should this idea have merit? Well it would restore the equivalency between matter and radiant energy. Just as a photon loses energy while traveling through space, so to would matter lose energy while floating in space. E=Mcc would be valid all the time.
(This idea is in my model described in Youtube use my name to see the videos John Kulick)