About two or three years ago, there was a fake "leak" circulating that alluded to a "farm pack" including horses-thus, I'm a little reluctant to admit this is real. However, there are just too many hints alluding to horses in Growing Together and related patches (i.e. my first infant had a horse-print onesie). Thus, they have to be coming soon, and I'm now inclined to say this is real.
Finally, the Sims I made based on equestrian/rodeo athletes, wranglers/ranchhands, and quite a few more things can have horses.
I am also VERY curious as to the sizes of the lots (which have to be huge), the premade Sims (as well as their horses), the architecture, and most importantly, the CAS. Near the top of the list--a better-looking Stetson, chaps, and better-looking modern Western shirts.