While I definitely would be game for this, I suspect they will not since Cottage Living adds both animal and rural elements. Yes, there is definitely much more to explore (for example sheep ranching, since it is not only cows that have this sort of rearing in the midwest USA). However, I doubt they will be willing to service very similar themes at the same pack level. If anything, we might get addendum content in lower pack tiers.
I also suspect if horses come, they will be in a specialized equestrian pack (I'd assume a GP, but there is some wiggle room).