The Amazing Mindthemoods!

An (admittedly not so minor) tweak to Elytra mechanics to try and make things a bit more balanced. Originally, I was going to implement Mojang's idea of only damaging Elytra when boosting with fireworks. This proved more complicated than expected, so instead, Elytra will now consume a (configurable) amount of EXP while the user is in flight, and will only take damage if the user's EXP is fully depleted. (At which point they'll take damage fairly rapidly.)

Elytra consumes EXP at a rate of a little over 1 orb per second of flight. (This is configurable.)
This scales with the player's velocity; maxing out at about 6 orbs per second at maximum firework speed. (This is also configurable)
When the player's EXP runs out, Elytra occasionally make hissing noises and produce bursts of soul fire particles to warn the player that their wings are taking damage.
When Elytra is very low on durability, it makes an incessant hissing noise, and emits a trail of soul particles, giving about a 10-15 second warning before breaking.

This has some pretty big impacts for gameplay, which I may or may not have tested thoroughly. Namely:

Elytra can still be overpowered if you happen to have an EXP farm- however, (unlike their current state), they thus still require some form of infrastructure as a mode of transportation: you either need sources of EXP at other destinations, or a big enough supply of Sculk/Experience Bottles to always ensure you have enough fuel. This is my biggest qualm with Elytra- with sufficient enchantments, they essentially allow the user creative flight, with next to no downsides.
Enchantments such as Mending, Unbreaking, etc; are now largely pointless for Elytra, as they'll only repair already damaged wings/slow the breaking process respectively. ...However, I might be convinced to add some enchantments specifically for Elytra. It wouldn't be too hard, for example, to add some form of boost enchantment that consumes extra-large amounts of EXP for a powerful thrust; or an enchantment that could rapidly burn through EXP to increase the Elytra's speed, similar to fireworks.

FLIGHT SPREADSHEET

A link to a spreadsheet to calculate EXP Costs and Flight Durations based on your selected gamerules. Download a copy to run your own calculations.

Soulytra Flight Calculator

TECHNICAL NOTES

The 'ElytraEXPConsumption' gamerule determines the duration it takes for the Elytra to consume EXP. This is set to 17 ticks by default.

The 'ElytraEXPQuantity' gamerule determines the amount of EXP consumed each interval. This is set to 1 EXP by default. (Hence 1.18 Orbs per second.)

And lastly, the 'ElytraProportion' value determines the amount of additional EXP consumed depending on the player's speed. This value is divided by ten and then multiplied by the player's current velocity. The default value, (seventeen), means that the additional EXP consumed is equal to 1.7 the player's current velocity, rounded down.

For more information, see the Flight Calculator.