Though limited creation has been a thing in this game and other online FF's, I completely agree that letting horns be their own selection would be most welcome.
That said...it might be a feature that arrives far later than Heavensward's release, while also assuming the variety of horns don't clash with head shapes and geometry of headgear. I'm not sure how much difference there is to the actual geometry of the character's different head models (if any), but that is something to consider.
I'm not saying this is a bad idea, all I'm suggesting is that it's likely not as easy as some assume.
That said...it might be a feature that arrives far later than Heavensward's release, while also assuming the variety of horns don't clash with head shapes and geometry of headgear. I'm not sure how much difference there is to the actual geometry of the character's different head models (if any), but that is something to consider.
I'm not saying this is a bad idea, all I'm suggesting is that it's likely not as easy as some assume.
