gold teeth
I mentioned something similar. A material swap for teeth is the easiest way to get that, but it would be great to see deeper customization. Varied geometry (presets like big canines/buck teeth/gaps, etc, are a good start), asymmetry, gum materials, applying all options to the upper and lower jaw independently, etc.
Want blue glowing gums? Okay. Each tooth a different color? Missing teeth? Clear teeth, with ivory vamp canine teeth? It could be taken so much farther than just a color swap with much of the same basic tech.
CDPR are intelligent people. I'm sure they've asked themselves "how many options can we get out of X functionality?"