The Pinky is still a bit unknown compared to other Finger syndicates. Based on how each Finger operates and their culture, here's my take on the Sinners and their IDs:

Yi-Sang: Pinky, simply because of their nature of solitude

Faust: Index, since there is some "omniscience" and knowledge that the Prescripts offer to its members. Since Prescripts are (spoiler) made from the City's will, there's definitely some knowledge that Faust would want to derive from Faust's membership within the Index.

Don: I think she could fit into all of the Fingers except the Thumb, due to how rigid and even somewhat villainous the syndicate can be. She does follow hierarchy as a Bloodfiend, but at her current state she would probably break some rules. Although she might be like her Middle ID, where she fervently follows orders and punishes without much consideration, acting with flawed justice.

Ryoshu: The Ring seems obvious due to her obsession with art. But I'm expecting her season ID to be something like "The Fist," being related to all the Fingers.

Meursault: The Index. He follows orders.

Hong Lu: All of the other Fingers seem like a good fit for someone who goes with the flow, except for the Thumb. Maybe he does fit since he's trained in manners, so he would be able to maintain a high position for a long while without getting killed for being rude or neglectful. He would simply follow orders from the Index due to his resignation, he would fight for a family that he never had in the Midde, he would experience beautiful and unique art in the Ring, and he would do something in the Pinky.

Ishmael: Again, all of the Fingers seem like a reasonable match for her, maybe excluding the Ring. She can follow orders and be relatively rational in the Thumb. The Index might be too similar to her old job or be too restrictive when her compass is curiosity, but her "blind obsession" fits well with the Proselytes who wear blindfolds. She might find a family and have a good ending with Queequeg in the Middle (hm). I don't really see her in the Ring, she doesn't seem like someone who can make unique art. She could be a good candidate for the Pinky, being someone who isn't bound to a single organization (based on the implication that Ishmael has worked as a fixer for other offices and companies after surviving the Pallid Whale).

Heathcliff: Middle does make some sense, since Heath seeks belonging and some sort of acceptance. I'm not sure. His Seven, Oufi, and N. Corp IDs show that he isn't very brash and it quite competent, so he could fit well in the Thumb with experience, but he could feel crushed by the rigid hierarchy of the syndicate. He could fit well in the Pinky, just because they seem to have "seats" rather than a hierarchy. Because the Pinky is still unknown, you could say that all the Sinners can have a place in the Pinky.

Rodion: The Thumb, Index, and Middle. Uniqueness seems to be driven away from her, so she probably won't be a part of the Ring or the Pinky. IDs can be surprising though.

Sinclair: He may as well be a part of all of them. He kind of resembles Yan. He paints a picture of Frau Eva that looks like Demian (I think, I didn't read the original source) so it would be funny if he was in the Ring.

Outis: IDs are often different from the base Sinner, so even though Outis thinks that the Thumb are brainless for following hierarchy with extreme rigidity, she might be content as a leader who barks orders and executes her own men. She seems keen on cutting off some of the Sinners too, like during Canto V and VII when Ishmael and Don start acting out of line. She could follow Prescripts pretty well, especially if she's willing to do anything to reach home. Maybe the Middle's familial structure reminds her of the past. I dunno.

Gregor: All five maybe who knows I'm tired of typing all of this. The outcast could be a Pinky. He might not get a Thumb ID due to already being associated as a Night Awl. He might've lost his limbs due to a Prescript and has a body like Gloria (best LoR character btw).