Grant Rodiek, a producer on The Sims 4 Expansion Packs has confirmed that Cats & Dogs WON’T be playable like in The Sims 3 Pets. He basically said that Pets will have a mind of their own, like in The Sims 2 Pets.
It was a think that was debated for months by The Sims Team but Grant is confident that the team has made the right decision of making Pets not playable.