We don't need to run around as KFC raw material all the time.
Make a glyph or a class skillbook like you did with treat form, and that should give you the cosmetic ability to go moonkin.
Alternatively, make it a talent like it was in vanilla, or like Incarnation: Tree of Life is now, then add Incarnation: Chosen of Elune on top.
Drawbacks: None
Advantages:
- Player Choice
- You can see your transmog
- This incentives running old instances for gear looks.
- See your face, and all the new options coming with Shadowlands
- Be cooler