HD Nagas would be sweet.
I would want warlock demons to be updated, and gnolls, but leave hogger with the current model, (he just wouldn't be the same )
The dragon models, because that will affect the mounts as well.
I'd like to see some of the Spider models updated. Mainly the forest ones with the fur.
Moonkin so it'll go straight to Moonkin forms for Druids, or Ethereals perhaps.
Armory: https://worldofwarcraft.com/en-us/ch.../dalaran/ryuji
Song that's currently stuck in my head: pretty much anything from Dance With the Dead
I don't satisfy myself with one.
All of them. No excuses.
Gnolls and Kobolds, they look sooooo bad compared to everything else early on.
Worgen. Their spines and legs are too bent up and it makes them look like they have scoliosis.
Oh, wait. Just read the question.
Hmmm.... Undead. They should look like putrid walking corpses, not Nancy Pelosi sans make-up.