WoWHead found some interesting new things in the Alpha/Beta. There are several new models for older, kind of mundane creatures. Lots of go-to critters like Rabbits, Squirrels, and Rats have updated models, along with Murlocs, Kobolds, Owls, Dragon Whelps, Eagles, Banshees, Makura (not, as they list them, Lobstroks, which are the Outland equivalent and... wait, does WoW have two different kinds of crab-people?) Felhounds, Basiliks, Keepers of the Grove, Dryads, Satyrs, Harpies, and Bears (oh my.)
Some of these were sort of inevitable - with the focus on ancient Night Elf territory, it makes sense that we'd get updated versions of a lot of the creatures they hung around with. We did see updated Ogre, Arrakoa, and Wolves in Draenor.
What's kind of cool though is that a lot of these models really look like pure updates, instead of redesigns. The Murlocs look unquestionably like the Murlocs we've seen in the past, only they look caught-up graphically to the rest of the game.
What I wonder is whether these models will only be used in the Broken Isles, or if they're going to go back retroactively and spruce up the old world. According to WoWHead, these models will not update the existing pets you have (though the Rabbit with blood on its mouth would have to be the Darkmoon Rabbit, wouldn't it?) Given how most of these are strict updates and not redesigns - looking as if you had just turned up your graphics settings or something - I don't really see a downside to populating the old world with much better-looking critters.