Well, it could be said that pigs, cows and sheep were purely esthetics for a long time to the point that they're like the generics of Minecraft. This is even more true with the sheep which until the sheering, didn't have much of a purpose. Even wolves/dogs have more of a purpose than cats which are kind of just there and are able to scare creepers.
I can even think of many purposes for mountain goats. Limit the population of sheep and cows to lower ground, and if you build something on a hill like a house and farm, likely the only thing you should encounter are mountain goats which you could fence in and which could have a dual purpose of being milked and providing wool. The challenge would be in milking and sheering them due to their headbutting.
I see that the next update will allow multiple resource packs to be used, which is interesting. This means that you could essentially use one resource pack for its textures, and one resource pack for its sound if the first one doesn't have sound of its own. If your favourite pack doesn't have a complete set of textures, then it would select the next pack in the list in the order of priority to use as that set of missing textures.