If we think of the geodesic that a photon travels as a rail, of possibly infinite length, that we can jump on anywhere, and ride at c until we want to get off, then the decelerating photon hypothesis has no hope.
If we think of that geodesic as a "prototype" geodesic however, then, the same way a line contains many line segments, the geodesic prototype should contain many actual geodesics.
Each actual geodesic is a segment of the prototype that has a maximum length of c/H (Hubble's length).
The velocity of a photon along that geodesic in v=c-HD.
If we think of the geodesic that a photon travels as a rail, of possibly infinite length, that we can jump on anywhere, and ride at c until we want to get off, then the decelerating photon hypothesis has no hope.
If we think of that geodesic as a "prototype" geodesic however, then, the same way a line contains many line segments, the geodesic prototype should contain many actual geodesics.
Each actual geodesic is a segment of the prototype that has a maximum length of c/H (Hubble's length).
The velocity of a photon along that geodesic in v=c-HD.