I like some of the Unique mount skins like the Humming Bird for Skimmer and the Deer for Jackal.
Next I would like a Unicorn/Pegasus hybrid for a Skyscale Mount skin.
not sure if some special effects could also be a thing. Maybe since there is already a fire effect skyscale. But a Running on a beam of light animation, when flying, for this would seal the deal for me.