Well it can be easily reskinned into a shadow apparition or whatever when a hound doesn't feel thematically fitting. I personally like it being the hound because the folkloric Black Dog (and probably because of the possible Malazan reference). Mechanically the ability in the original UA was pretty interesting and definitely had its uses. It was a summon ability, without any concentration involved, that came with additional benefits and most importantly it (and the darkness ability) were both alternate ways to use sorcery points.
So about other sorcerer subclasses. The favored soul (maybe with a name change, to differentiate it from the 3.5 class) is probably in, it was popular, it appeared among the revised sublasses and so on. We know thats its possible, that the fighter gets 3 sublasses from the 25 new, so its also possible to the relatively subclass starved sorcerer. Stone sorcerer has some potential to be one of them, but was it popular enough for that?