On one hand, I could completely understand if it doesn't have seasonal skins.
On the other hand, it is a very unique feature only a handful of animals have and I would be surprised that Frontier didn't think of that when planning the animal for the pack. So looking at what they've done in other games, especially JWE (I am aware that JWE and PZ are on slightly different versions of the engine, but they were much more alike than PZ and PC), I think there is some evidence that Frontier can do such a feature.
Indominus can change its skin color dynamically based upon parameters, aka when it walks into a forested area it turns green. JWE and PZ both use a similar color maps, because variants in PZ are also made dynamically. So we know there is a way to dynamically change the color hue of an animal based on parameters. Given that time moves so fast, I think it's not going to be time based but much rather temperature based and more so based on the condition on whether it snows or not. I don't know how they would tackle the fur length, as a different model isn't really needed, all it requires is a different fur shader with longer fur.
All in all, I'm still torn on whether they'll do it or not. There is a precedent for it, and I personally find the change much more fitting than animals loosing antlers ( which would require model switching and even though it is a thing for scenery objects, I don't know if it's possible for animals). I also remember that there were a lot of people who were absolutely convinced that the meerkat would either only dig with an enrichment item, but a looooot more people were downright sure of the fact that the meerkat wouldn't dig at all. And yet, as always; Frontier did deliver.
So I'm not sure. I don't know if they'll do it and I wouldn't mind it if they didn't; but on the other hand Frontier does often have tricks like that up their sleeves so I wouldn't be surprised if fur changing becomes a thing.