As much as I like and enjoy the korasi, this thing is gonna be 100% dead content simply because korasi holds no other use other than PK only. Yes it's a very unique item but it will never see the light of being anything other than an aesthetic and will only be used for fashionscape or will collect dust in the bank. Making it a donation only option as of current was probably the wrong move to make see as this probably won't be a sought after item and to me only holds the value of what you put in, which is $5 according to it's donation option. Regardless of what people say about it it will always be worth that much until given an actual purpose. Korasi should probably have been a minigame strict item or a whole new content such as a new boss or maybe a custom raids 3 item, even possibly introducing custom dungeoneering (not suggesting that just saying that's the only valid reason i could see this being a part of a minigame hint hint the ring of vigour that partners with my friend here). My actual suggestion is adding another boss to the wilderness other than hulk that drops korasi, ring of vigour, void deflector (Not many people know what deflector is so i'll explain some of these items), and the other two curse variations of turmoil for ranged and mage ( Torment and Anguish ).
For those who don't know what other items do
Void Knight Deflector
It's an item that goes into your shield slot that allows you to use the full effect of void while being able to substitute one piece of gear with whatever you please as long as you're wearing it.
Ring of Vigour
This item pairs with the korasi's sword although it's not necessary. This reduces the special attack of any item by 10% of the original consumption.
Torment and Anguish
These prayers are pretty much turmoil but with magic and ranged. Yes these are EOC but it doesn't mean they can't be coded are OSRS prayers like we already have from turmoil and soulsplit.
As for boss suggestions I have a lineup of different things that can be used as hosts for these items:
Skotizo which I think would be a perfect candidate seeing as you need dark totems to summon him (which can be obtained from the kourend catacombs on slayer tasks and you would have to summon him). There can be dark altars placed around the wilderness and be summoned using the totems that would alert the server of his summoning, but not his location.
This one is pretty weird but i think it would be a valid option if his model could be transferred into the game. By technical terms the decaying avatar and the avatar of destruction are the world bosses of soul wars and we very very difficult to take down by yourself.
Originally the korasi's sword would come from a quest line having to do with her in the first place in the quest "the void stares back" where the korasi is a must for this fight. Instead of having penance queen "requiring" this, the korasi would instead do increased damage to the penance queen and stunning her when using the special attack on her.
I will make more suggestions in the future on this and even come back to edit this for more ideas, stay tuned. Let me know what you think and maybe we can discuss about it.