While I don't have much evidence for this theory, the more I think about it, the more I start to believe in the idea that Iguin is another host of the silvertree.
From Iguin adding his own blood to the bottle of ink and the theory that he and Qifrey are clones or at least share more than what meets the eye (pun intended), it just seems fitting for Iguin to be another silvertree host who has also lost an eye. The imagery of one eye is heavily present with his character similar to Qifrey.
If Iguin is indeed a silvertree host, then he could parallel Ininia. Ininia and Iguin are two silvertree hosts who have never had the silvertree emerge on screen compared to Coustas and Qifrey, who have.
On a different note, it's quite intriguing to see the similar mannerisms that Iguin and Ininia share. Two seemingly aloof witches who view forbidden magic as the right way to do things. They are witches who are incredibly critical of the witches code and use forbidden magic to reverse the effects of Dagda and Euini's injuries and transformation. The two witches try and make Coco join the brimhats with Iguin calling Coco their saviour and Ininia calling Coco a friend.