Thanks to community modding tool Sims 4 Studio, it was discovered that some brand new CAS Parts have been added to the game, but not yet available for use. Lips Rings (left/right), Nose Rings (left/right), & Brow Rings (left/right), are CAS Parts that show up within the tool.
These CAS Parts are by no means officially confirmed, but they are showing up within the code and unlocked by Sims 4 Studio’s program since 2015. Perhaps we can expect to see these items added to the game in the future, or never at all.