Hmmm well I tend to think there aren't any simply because coding them for backround would be a pain, plus it's more stuff for the game to have to track.
Though honestly a cat big enough in proportion to kill molerats like housecats kill normal rats could be interesting.
At any rate cats are first and perhaps most important of the three "Companion Animals" of humanity. The three animals that are aguably are closest friends/most useful/closest to our hearts.
Cats are arguably a cornerstone of civilization because they tend to hunt down and kill vermin which can get into food supplies and spread disease. While there were incidents during like The Black Plague with people thinking cats were responsible, cats arguably are one of the things that allowed large cities to be build and food to be stored as civilization was coming up.
Horses are arguably a cornerstone of civilization because they serve a useful dual purpose of being able to move very heavy things for people, as well as carry man long distances, very rapidly. Perhaps the least useful of the three in modern times, but integral for us coming up.
Dogs are arguably a cornerstone of civilization because they can help man in a lot of ways. Protector, hunter, alarm system, and even emergency food supply (which can be said of the former two as well). Dogs can be insanely loyal and while they don't nessicarly do anything a person can't do without them, the assistance of a dog makes many tasks much easier. Even today the intelligence and loyalty of dogs makes them useful for helping handicapped people. A dog can be used for things that the above two companion species couldn't even be conceived of doing.
At any rate if like humanity was going to colonize a planet, those are the first three animals/top priorities to bring along. Some might disagree, but I don't think I'm the first one to say this.
If they ever do add more animals having a ridable horse, and maybe some kind of cat (though functionally I have no idea what purpose it would serve in the game) would be nice.
While I'm not doing mods yet, I did see one mod on Fallout Nexus which adds a town to the game that you can build up for Wastelanders and such. If such mods become popular and more advanced, having cats to hunt down vermin and protect the food supply/prevent people from getting sick could be a part of the sim. Cats being a low-tech solution to disease spreading/grain eating animals.