Elytra are hard to find, but once you find one, you can sustain it indefinitely by repairing it with Leather, one of the most commonplace items in the Overworld. Combined with Shulker Boxes, this makes other transportation systems such as Minecarts and Horses somewhat obsolete.
My idea is that high-speed flight should be somewhat expensive to maintain but still be renewable (and not get nerfed by adding mobs into the sky), and Dragon's Breath fits that criteria. It's not terribly hard to get, but definitely more challenging than simply killing cows. This would also give Dragon Breath another use since Lingering Potions aren't that useful in Survival. Instead of physically soldering the item onto the tool, Dragon's Breath would cause the Elytra to heal magically.
In addition, Mending should be less effective on Elytra and only heal 1 durability per XP orb instead of two. However in exchange for this, Elytra repair costs would go up slower, and would max out at 39 levels instead of becoming "Too expensive", so that you don't have to grind for another rare structure unless you want to reset repair costs.
You can only repair any item just 6 times on the anvil before it becomes too expensive; anybody would rather use Mending instead so you don't even need any materials (though I think it should work like renaming did before 1.8, making you have to use materials to repair items on the anvil along with the repair costs depending on the item and enchantments):
After six workings, the penalty will be 63 levels, making any further repair or enchantment impossible in survival.
I believe Elytra were exempt from this, allowing you to repair them using Leather as many times as you wanted, because of their rarity in comparison to normal tools or armor. This is also the reason Elytra don't disappear when they lose all their durability.
Elytra can Become "Too Expensive" to Repair at Anvils
Resolution: Invalid
So, 15w42a was released today, and it looks like that Jeb and Mojang have decided on a new system. The Mending enchantment was introduced. An item with this enchantment will have its durability restored, if needed, as the player collects experience. Exp. goes to the mendable item instead of the player. Therefore, elytra can be infinitely repaired if it has Mending. However, enchanted books with Mending will only be found in the world, like elytra. Locations haven't been implemented nor confirmed at this time.
The not breaking/disappearing when losing all durability has been present since they were introduced I believe and was probably added because they are much more valuable than other items.
Like others have mentioned, using Mending is still a better option. Additionally, you can easily get over 64 bottles of Dragon's Breath each time you fight the Ender Dragon, so this change wouldn't make repairing the elytra much more challenging.
For the record, I found Elytra maintenance so annoying (and so rare) that I built a command-block shrine on the only End-City boat we've found on our server that gives any player that touches it an unbreakable Elytra. So they still need to get to the End and find that city, but once they've done that, they can actually enjoy it instead of worrying about it. Also so that more than one person on our server could play with them.
As an Op, I spent several hours in creative mode cruising the End looking for End City ships, and never found another one. It still seems incredibly dumb to introduce an item (with an entire flight mechanic) and then put so many ridiculous limits on it AND make it so rare that it is impossible to have one until after spending several hours in the End. Or days, if one is unlucky.
Elytra are hard to find, but once you find one, you can sustain it indefinitely by repairing it with Leather, one of the most commonplace items in the Overworld. Combined with Shulker Boxes, this makes other transportation systems such as Minecarts and Horses somewhat obsolete.
My idea is that high-speed flight should be somewhat expensive to maintain but still be renewable (and not get nerfed by adding mobs into the sky), and Dragon's Breath fits that criteria. It's not terribly hard to get, but definitely more challenging than simply killing cows. This would also give Dragon Breath another use since Lingering Potions aren't that useful in Survival. Instead of physically soldering the item onto the tool, Dragon's Breath would cause the Elytra to heal magically.
In addition, Mending should be less effective on Elytra and only heal 1 durability per XP orb instead of two. However in exchange for this, Elytra repair costs would go up slower, and would max out at 39 levels instead of becoming "Too expensive", so that you don't have to grind for another rare structure unless you want to reset repair costs.
You can only repair any item just 6 times on the anvil before it becomes too expensive; anybody would rather use Mending instead so you don't even need any materials (though I think it should work like renaming did before 1.8, making you have to use materials to repair items on the anvil along with the repair costs depending on the item and enchantments):
In fact, I believe they originally added Mending just for Elytra, with other items able to receive it as a bonus.
TheMasterCaver's First World - possibly the most caved-out world in Minecraft history - includes world download.
TheMasterCaver's World - my own version of Minecraft largely based on my views of how the game should have evolved since 1.6.4.
Why do I still play in 1.6.4?
Most people use mending nowadays, this won't make a difference.
Not according to https://bugs.mojang.com/browse/MC-89980:
The not breaking/disappearing when losing all durability has been present since they were introduced I believe and was probably added because they are much more valuable than other items.
TheMasterCaver's First World - possibly the most caved-out world in Minecraft history - includes world download.
TheMasterCaver's World - my own version of Minecraft largely based on my views of how the game should have evolved since 1.6.4.
Why do I still play in 1.6.4?
Like others have mentioned, using Mending is still a better option. Additionally, you can easily get over 64 bottles of Dragon's Breath each time you fight the Ender Dragon, so this change wouldn't make repairing the elytra much more challenging.
Check out my suggestions! Here is one of them:
No support.
For the record, I found Elytra maintenance so annoying (and so rare) that I built a command-block shrine on the only End-City boat we've found on our server that gives any player that touches it an unbreakable Elytra. So they still need to get to the End and find that city, but once they've done that, they can actually enjoy it instead of worrying about it. Also so that more than one person on our server could play with them.
As an Op, I spent several hours in creative mode cruising the End looking for End City ships, and never found another one. It still seems incredibly dumb to introduce an item (with an entire flight mechanic) and then put so many ridiculous limits on it AND make it so rare that it is impossible to have one until after spending several hours in the End. Or days, if one is unlucky.