When they started doing horses before cats and dogs came out, they were programmed as cats and dogs were. I think it's save to assume they'll take up a household slot, can be painted in CAS and will roam freely like cats and dogs do. I guess they'll only randomly spawn in certainly lot types in the new world. If there are unicorns, those might spawn at the BG Secret Lot that is accessible through that tree in Willow Creek. At least that would make sense as that place fits perfectly and cannot be used for much else anyway, IT would Help them spare ressouces for other stuff. If there shall be fairies, those could spawn there either.
