Here is a Youtube video about all the datamined gnome customizations so far. These include three new skin tones, a bunch of new hair colors (including vibrant blue, purple, orange, teal, and green), several new eye colors, along with the two female gnome hairstyles that were added in Cata (or WoD?) but never implemented in game. Cool new jewelry textures have been datamined, but the meshes are not available to make them viewable yet:
With the new darker skin tones, I hope we also get some fun curly hair textures for gnomes, as well. The new datamined human hairstyles are great so far. Human women now have the option for a curly bun puff, and I think it would be adorable for gnome women to have curly pigtail bun puffs, for example.
Other customization options I would like to see for gnomes include two currently NPC-only skin tones. These are the leper gnome skin and the gray, tattooed cultist skin. With the cultist skin and red eyes, you can get kind of close to a gnomeferatu appearance. I hope we can have violet eyes, too. These are the NPC-only skins:
