The reason none of those explanations works is because of a misunderstanding of the term "red shift". Red shift doesn't mean the light becomes more red; it may do so, or it may become less red.
Red shift is the same thing as the Doppler Effect. You know how with train whistles and police sirens, they are higher pitched when they are approaching you and lower when they are moving away? Of course, the whistle doesn't change pitch just as it passes you.
Let's say the train's whistle is at 1000 cycles per second, and the train is moving towards you at 10 metres per second. It sounds its whistle when it is 100 metres away, and keeps sounding until it is 100 metres past. That takes 20 seconds in all.
But the speed of sound is about 330 metres per second. So the very first sound from the whistle takes about a third of a second to reach you. The first 10 seconds worth of whistle is squashed into 9.7 seconds - when the train is right beside you, the time taken for the sound to reach you is negligible.
And similarly, as the train moves away from you, it takes 10.3 seconds for all the sound to reach you until the whistle cuts off when the train is 100 metres away.
So in the as the train moves towards you, all the sound is shifted upwards in pitch by about 3%, to about 1031 cycles per second, and as it moves away the pitch drops by about 3%, to 971 cycles per second.
Now, here's the thing: If the train played a tune on its whistle rather than a constant tone, the same effect would apply to all the notes, and to the durations of the notes.
How does this apply to the Cosmological Red Shift? I'm glad you asked!
Light emitted by stars is neither a single pure frequency nor a perfect continuous spectrum. Every chemical element has a number of characteristic frequencies at which it can emit or absorb light - these frequencies depend on the number of electrons in the atoms.
Here is a picture of part of the spectrum of our Sun.
These spectral lines are very useful because they let us detect what elements are present in a given star. They also provide a marker as to what frequency the light was originally emitted at, and allow us to tell if it has been shifted by the Doppler Effect.
So if we know of a set of lines that look like this:
RED || ||| | | || || || | | | ||| BLUE
And when we look at the visible light of a particular star, we see:
RED ||| | | || || || | | | ||| | | | BLUE
We can see that by sliding the spectrum of the star to the right, suddenly all the lines match up. That means that the light has been shifted redwards, what we call a "red shift".
The Cosmic Sunset won't do this; it just decreases the amount of blue light and increases the amount of red light.
Degrading Light won't do this either. We'd simply stop seeing the spectral lines at the blue end; the ones at the red end would remain in place.
Multi-Speed Light wouldn't do it. I don't see how multi-speed light would have any effect at all (in this situation).
One thing that works is the Doppler Effect.
Another is the "Tired Light" conjecture, which suggests that over very very long distances, light gradually loses energy. Unfortunately, that contradicts Relativity, Quantum Mechanics, and the First Law of Thermodynamics, so it's not taken very seriously.
