Hi Brett,
I look at coprophagy of dog feces as evidence of Spleen deficiency, as you suggested - that is, an effort by the animal to compensate for its own digestive weakness by eating something pre-digested.
When dogs eat feces of herbivores - especially dried feces from rabbits and deer, etc. - I see that as them try to supplement their microbiome with bacteria that use plant material to seal the gut wall and elaborate propionate to help regulate the immune system. Those kinds of needs often need to be filled in Shao Yang disharmony dogs.
Soil consumption can reflect that, too, or can be indicative of Blood deficiency as can (potentially) the consumption of dry wall.
Lastly, I see animals eating fabric and grass as having Phlegm issues (or perhaps more rarely nausea issues from other causes such as Yang Ming dryness).
I think that covers the gamut. Hopefully, that helps!
Steve