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.