Please make Moonkin Form a cosmetic choice like Treant Form is for Restoration Druid.
The champion Druid of Azeroth should not be required to use a Moonkin Form to be able to cast powerful spells at this point. Turning into a Cat or Bear makes much more sense because you’re using claws, teeth, and primal fury to attack your enemies. Spellcasting is something any humanoid can do proficiently, as far as lore reasons go.
As for mechanical reasons, the armor bonus is super negligible and honestly not even noticeable, 10% damage increase is really not even THAT big of a number if you think about it, and the chance on being hit procs of Starfire could be just a Balance Druid passive in the spellbook with no need for a form to activate that. (Also, the extra GCD going into Moonkin Form feels clunky which is just a personal gripe of mine.)
As far as being immune to Polymorph effects in PvP, I can’t see why there couldn’t be a PvP talent added to the game to facilitate that benefit. Or they could even add that effect to an already existing PvP talent. (Or once again, a Polymorph immunity could become a Balance Druid passive in the spellbook baseline, though I’m not certain if that would be too overpowered.)
If Moonkin Form was a cosmetic option, players would be able to customize the way they wished to present themselves in game. Whether they would still choose to use Moonkin Form if it became optional or had a personal preference to remain in humanoid form. I think giving players the agency to customize how they wish to appear in game is something Blizzard would agree is important.
Blizzard has already taken at least some small baby steps towards this goal when they made it so Shadow Priest’s Shadow Form now shows your character model even more than before with the Glyph of Shadow. (I would like if Shadowform was an outright cosmetic form like Treant Form as well by the way.)
I want to say as well I think all the new datamined 10.2 Guardians of the Dream Moonkin Forms look wonderful, and if Moonkin Form were to be made cosmetically optional I would still use those forms from time to time on top of my humanoid caster model (Night Elf).
I would love to finally be able to fully enjoy my Balance Druid without the arbitrary cosmetic requirement of Glyph of Stars, and from what I gather, I think a lot of people feel the same way.