Speed of light...

What would happen to the red shift of light for very distant objects if
there was some sort of phenomena related to the very distant leading
edge of the remnants of the Big Bang? I guess I'm thinking that on a
classical scale when light passes through a material, it slows down in
that material, and these effects are definitely observable. Of course,
there are other phenomenae (i.e., absorbtion spectra) that are also
observed, but I'm conveniently assuming that the scale of things cancels
them out.

I guess what I'm trying to articulate is what if the concept of "dark
matter" or whatever does exist Way Out There, and while not directly
affecting light like we see with classical optics (i.e., chromatic
aberation, absorption spectra, etc), there are manifestations on the
behavior of light at a large enough scale that are analogous to some of
these behaviors, but because at the distances involved some of them just
get cancelled out, and what we are left with is just red shift?

What if way out at the edge of our known universe, there are objects
even more distant than what the edge of the universe is at right now,
and their light has been coming through the leading edge of the Big
Bang, but somehow been phase-shifted to make it appear that they're
going away faster, but they really aren't, and that because we do not
have a portal for light that does go purely through a vacuum for 15
billion light years, that it can't really be directly observed?

I guess I'm thinking of something like a very slight difference in
"universe vacuum density" between where we are at now, the outer limits
of the Big bang, and whatever lies past it, that might cause an effect
like this with light that has passed through it?

What happens if light is passing through a wave front in a very slightly
non-full vacuum universe, could the motion of that wave front distort
light in the same way as if that light was coming straight through a
pure vacuum from a source moving the same way?