One issue that I've seen come up multiple times recently is that certain items are non-renewable in the world, and those resources have all generally been claimed. This creates an unbalanced market for certain items ...
    *cough* Elytra *cough*

There are many ways to try and remedy this, like resetting the end, or adding sponges to vote rewards, but those have their own inherent problems. While I'm not against any of those ideas, I wanted to offer another potential alternative.

For all of the rare non-renewable items, they are difficult to obtain because they offer a challenge. Elytra involves end raiding, sponges involve fighting Elder Guardians, even Heart of the Sea involves fighting drowned and usually a bit of searching. So to keep with that, I'd want to add rare items as renewable drops, but with their own challenge involved.

So I want to make new, theme'd Treasure Goblins.

Of course, this can entail a LOT of specifics, but I don't intend to cover it all here. If you like the concept, please support it, and we can discuss and figure out all the details later on. But i have a few potential examples below for goblin additions. 

Amethyst Goblin:
- Purple Armor
- Drops 1 Elytra, 10 individual shulker shells, and lots of partial stacks of various purpur blocks and some end rods

Prismarine Goblin: 
- Cyan Armor
- Drops 1 Heart of the Sea, 10 individual sponges, and lots of partial stacks of various coral and some sea lanterns

Obsidian Goblin:
- Black Armor
- Drops 3 Wither Skeleton Heads, partial stacks of quarts, obsidian, and TP eyes, and some ghast tears

Treasure Goblin:
- Gold Armor
- Drops the same stuff still

I like this idea, Bowman!

Themed Goblins, with drops and maybe small thematic changes around skills & attributes, would be fun.

Right now some fights have a fair number of goblins, and I see a lot of Ruby Keys dropping, so I've been thinking of toning that down some and perhaps this would be a good alternative to Ruby Key drops. Are you thinking 100% drop chance for elytras/hearts/skulls?

 

Maybe yes, maybe no for 100% drops. I'm not sure, because it'd likely have to be balanced with other potential changes. The secondary version of this was to have entirely different versions of the dragons with craftable dragon-spawn eggs that would be better suited to small group fights so you can farm the item you want, although slowly. 

So there's a lot of ways this drop could be implemented, but I don't know what a good rate would be. It would likely be different for each goblin and each would need tweaking, and it would depend on how you may change the rate of the goblins. 

The current scenario I have in mind has the following: 
Multiple theme'd dragons, each with different "magic", different special mobs (like the Ruby Skeletons) and a chance to replace the Treasure Goblin with their own specific goblin. The Dragon would also have an increased chance to drop the items on death. To summon these, you'd use a special crafting recipe that create the spawn egg, leaving the Ruby Dragon to still be donation-only. Recipes TBD, but I have ideas as well that are intended to match the theme'ing, but also intended to be difficult, since you'd still need the Crystals to summon them. To give one example (I'm particularly fond of a Prismarine/Sapphire Dragon myself), to get the Egg, you'd need 4 Tridents, 4 naut shells, and 1 Lapiz Lazuli block. Ideally, each dragon would include something that should prevent, or at least slow, mass farming.

Assuming all the goblins that spawn are for a single type (Amethyst, Prismarine, Obsidian, or Treasure), the TOTAL drops per dragon fight would be something like this on average:

If ALL are Amethyst: 2 Elytra, 16 shulker shells, 4 stacks of the other items
If ALL are Prismarine: 1 Heart of the Sea, 16 sponges, 4 stacks of the other items
If ALL are Obsidian: 3 Wither Skulls, 32 obsidian, 32 quarts, 16 tp eyes, 8 ghast tears

Of course, these are arbitrary and it depends on difficulty, and the spawn rate of special goblins, and any of these mechanics are even used. But that's very close to the full idea I had in mind. To keep it simple and start with step 1 though, I wanted to focus upon the idea of creating a challenging combat-based way to farm these resources to help with the server's economy.