Foxes dont follow a hierarchical system like dogs, cats or horses where there is an Alpha (the owner of the animal) whom they fall under in the pecking order.
Foxes like to shit and piss all over everything and burrow Into couches. Good luck with the fox thing.
None of them really have a hierarchy at all. Dogs, cats and horses are usually just a breeding pair and their offspring. Actually foxes are the only animal you named that does live in a structured hierarchy.
The guy that claimed it later proved it wasn't true and has spent the rest of his life yelling about how he was wrong. With way too many people not listening. Wolves just exist in social groups.
The study was on captive wolves, so it was not accurate to wolves in their natural environment. All it shows is that if you restrict wolves to a very small amount of territory, they will fight for dominance, probably because they think it means food scarcity.
I personally dont think we're close to fox total domestication however. It seems like we've selective breed a human friendly temperament but there's more to it than that for the sake of pet-ness that I'm sure people like to have. That is the main point in my OP. They love to mark, burrow into furniture and cause other problems. Those issues I think will be harder to alter than temperament. Probably not in my lifetime or most of ours in my opinion.