On the point of horses being 'customisable,' you'll be able to choose exactly how your horses look in Create a Sim, but if that's not your thing, you can also just rescue or buy one. It being a pack all about horses, you won't be surprised to hear that you can raise, train, and form special bonds with your horses that the leaks call 'customisable members of your family.' While the main (mane?) draw is being able to care for a horse, you can also look after mini sheep or mini goats, and your Sim can earn money by selling homemade nectar too, a returning feature from The Sims 3.
According to the leak, the expansion pack is due out July 20, just under a month away.