Horse armor is a deeply... unique implementation, as far as equipment is concerned. Rather than having an armor slot, it's treated as a custom inventory slot that only respects armor attribute gains.
Enchanting horse armor is an intuitive way to invest in your favourite horses, and thus horse armor should be updated to respect enchantments placed upon it.
This may require adding a feature that guarantees horse armor drops on death, as this might not be the case currently. Some reasearch is required.