This was changed on purpose! But never fear, it will return (hopefully next patch). I thought it was going to go in today, but we ended up needing to revert it. We are careful not to overwriting things in spells_us.txt. And overwriting the spell would have broken the item, not removed the textures. Pet appearance is like any other npc, it is handled in the database but can be affected with scripts.
I removed it because there was a bug with setting appearance that wasn't noticeable until I tried to use the functionality on pets. Although you may have seen the textures with old models, they did not work with new models, and robes did not work for either model. Many people prefer old models, but it is important to check both. The bug was actually pretty annoying and you can thank Jumbers for finally solving it (almost). I have been tinkering with these swarm pets for quite a while now. Sometimes things turn out to be more work than you think. It was probably too much time spent on something small, but once I started, I wanted to finish.
Halflings and gnomes got not only the textures but a bunch of new pet weapons. Using a weighted random these pets will have all the 'classes' for those races (in appearance only, they will all remain warriors). Tint is possible, but it would mean a change to the codebase as well as the database entry to allow a single, non-random color. There is a way to have random tints or even copy the specific armor and tint of a player, but that method is not compatible with pets.
Other swarm pets were not neglected! They all got fun little quirks to their appearance. Wisps are all different colors, leeches are different sizes, and you may find a new appearance for some pets in certain zones! I even made a temporary Halloween-themed swarm pet that will be given out later in events.