For all we know, it could be more than just dogs and cats. Maybe an active Veterinarian career which will work the way GTW doctors should have worked, with a place you can take your pets when they're sick or for grooming. Maybe pet shops, with the ability to own/run your own if you have GTW installed. Maybe even werewolves -- they made the best pet trainers in Sims 2. The only thing we're pretty sure about is that there won't be horses -- and how do they really work in a closed-world where you ride two steps and are immediately transported to your destination? I'd prefer them in a farming/rural pack, maybe with a special lot where you can board them then go to ride and train them, and compete with other Sims in racing or agility drills.