Interesting read but they provide no mechanism for decreasing frequency.
The frequency of a photon changes due to relative velocity of the source and observer (red shift). This means that the energy of the photon has changed at the observer.
This theory says that if a photon loses energy after travelling great distances then either Plancks constant has to change or the frequency has to change.
Or it could be expansion of the universe and expansion of the fabric of space that causes all observed red shift. It is difficult to set up an experiment.