Something I’ve seen played with a little in art but never in fic is running with the idea of the healers literally being dolls and showing some physical effects of that.
I especially want to see it combined with the idea that all three are completely different toys, made of different materials.
Personally, I enjoy the headcanon that doll Haruspex is made of leather (easy to scratch and scar if handled roughly but ultimately tough enough that a little cosmetic damage isn’t going to permanently destroy it, once-living skin cut away from the flesh of a body, specifically part of a cow, one of the earlier materials humans figured out how to work with in most traditional crafts), while the Bachelor and Changeling dolls are porcelain (expensive and “high-class”, inorganic and cold to the touch, harder than leather but also much more fragile, delicate when whole but cracks into something sharp and dangerous when it breaks) and cloth (soft and easy to rip and tear but also much easier to repair in a way that neither porcelain or leather are, can also be “of the earth” at one remove if you’re dealing with thread spun from an organic fiber like cotton or wool, has some fun mythological associations with destiny and prophecy a la the Fates weaving the threads of mortal lives) respectively.
There’s outright a line of dialogue where Dankovsky tells Artemy about them being toys, and he responds with: “You are also better-crafted than me, oynon. Take a look at us-a closer look. You are probably right about me, I'm not a toy to keep-unbending, leather-made, old, and shabby. You, on the other hand, are an entirely different thing! I'm surprised they're playing such a bad game with you...”
It’d be really fun to see something from the perspective of an NPC getting a brief look at something deeper, or one of the healers observing the other two, for that unsettling ambiguity- the Haruspex has tough, leathery skin? Well, not so surprising for a man who works heavily with his hands, but it’s odd to this degree... The Bachelor has always been pale- but has he always been quite that pale, so literally bloodless and dead white? You see the Changeling playing cat’s cradle with some string, but it’s hard to tell where the string is coming from- can it be that a loose thread in her fingertips has unraveled?
Or if you wanted fluff but Weird And Surreal (and why wouldn’t you, really) you could do something with the healers taking care of each other when their... unique conditions act up. One of the others carefully stitching together a ripped seam on Clara, or gripping Artemy’s hands until he gets feeling back in them.
I think Jiang Cheng is actually similar to Lan Wangji in that he also shows affection through giving gifts, though for mostly different reasons.
Like, Jiang Cheng’s demonstrably bad at expressing his feelings with words, and I also think that the most positive aspect of his own personhood, for him, is his status and power and wealth. That role he’s inherited, and the security that comes with it, are the cushioning for the festering pit of self-loathing inside him. And so his outward behaviour towards other who matter to him often manifests as spending money on them.
This manifests in a particular way with Wei Wuxian post-canon, because Jiang Cheng hasn’t lost his competitive impulse towards him and subconsciously feels his money and position give him something of an edge over this person he’s always been compared unfavourably to. Also he’s just in major “WE CAN’T LET WEI WUXIAN KNOW WE LIKE HIM” mode and so he defaults to passive-aggressively dragging him off to the tailor shop saying “you’re too scruffy, you’ll embarrass me dressed like this” and then commissioning five expensive sets of robes for him.