First off: read this. It would be informative to you.
Second: the main point of races is being cosmetic, with racials being mostly secondary. Plus it's easy to create 3-4 abilities that have nigh-negligible impact in gameplay save for cosmetics. For classes, it's the other way around: cosmetics are mostly secondary, while its abilities and mechanics are the focus point.
Class skins would have different graphics and animations, while keeping the mechanics of its "parent class" intact. Class skins would also have different NPCs attributed to them. The druid class would not have Mekkatorque as one of its representatives despite it being the representative of the tinker class skin, for example.