I believe Blizzard, especially with their class importance they will to bring together with Shadowlands, should focus more on DH customization: spells and ability effects should adapt to the tattoo color, aswell as demon form aesthetic features: Blizzard should let players customize metamorphosis looks, colors and effects a bit more, such as possible hair style and armor pieces.
Take Leotheras, for instance: I wish I could have my DH look like him, darker and more shadow themed instead of all of that forced fel green haunting every movement of mine, no matter how I choose to color my tattoos or warglaives. Plus, once you hit on metamorphosis, you look exactly the same as any other DH.
Please Blizzard, bring some customization to DH.