There are missing items:
Issue # 1:
Dyeable & Craftable Leather Horse Armor. Also make note that you would need to add the ability to wash your dye's out at a filled Cauldron. (Similar to how Leather Armor currently works for players.) Should be repairable with Leather.
Issue # 2:
Craftable Chainmail Horse Armor. Should be repairable with Iron Ingots.
Issue # 3:
Craftable Iron Horse Armor. Should be repairable with Iron Ingots.
Issue # 4:
Craftable Gold Horse Armor. Should be repairable with Gold Ingots. Also should not be more effective than Iron. (Similar to how Gold Armor currently works for players.)
Issue # 5:
Craftable Diamond Horse Armor. Should be repairable with Diamonds.

I would also like to state that I put "Craftable" very plainly infront of every item, as currently it is not craftable and finite. Most maps only have a single stronghold or few "dungeons" near the spawn, and large multiplayer servers would never be able to support new players being able to obtain these items. I feel that is a VERY BIG issue with these servers, especially those who plan to play legitimately on limited map sizes (for player interaction purposes, as it is very important as a part of MultiPlayer that the world not be "infinite" since Servers could never get that many people. Also noting, that while my server has had 50,000 users since January, they would still have probably explored a 32km x 32km map for all usable Horse Armors by that time, and it would be like finding a needle in a haystack at that point.

I present a valid argument for this being an issue and not "intentional mechanics" and would like to pursue with reporting it as such. If this Issue is closed for a non-related reason I would be extremely unhappy with this outlet for information to get back to developers.

I shall now use tags to identify the problem and related topics it is currently afflicting. Such as crafting. Armor. Map (regarding size.) Size (regarding maps.) Multiplayer (regarding map size, and player populations.) and Horses (for the very obvious reason of this entire Issue post!)