During the scene with Cabbie, Sherlock has him beat, but he accepts Cabbie's invitation to play the pill game anyway. It's this final acceptance that pushes Watson's ultimate change.
When they're at the restaurant (around the 50 minute mark on Netflix), Watson and Sherlock have this exchange:
Watson: People don't have arch enemies.
Sherlock: I'm sorry?
Watson: In real life. There are no arch-enemies in real life. Doesn't happen.
Sherlock: Doesn't it? Sounds a bit dull.
Watson: So who did I meet?
Sherlock: What do real people have, then, in their real lives?
Watson: Friends? You know... people they know, people they like, people they don't like. Girlfriends, boyfriends.
Sherlock: Yes, well, as I was saying... Dull.
Watson: You don't have a girlfriend, then.
Sherlock: Girlfriend? No, not really my area.
Watson: Oh, right. Do you have a boyfriend? ...Which is fine, by the way.
Sherlock: I know it's fine.
Watson: So you've got a boyfriend then.
Watson: Right. Okay. (chuckles) You're unattached. Just like me. Fine. Good.
Sherlock: John, um... I think you should know that I consider myself married to my work, and while I'm flattered by your interest, I'm really not looking for any--
Watson: No, I'm... not asking. No. I'm just saying, it's all fine.
Sherlock: Good. (meaningful pause) Thank you.
While I would say this is mostly an RS scene, it's also the most intimate look we get at Sherlock outside the realm of solving the case, and it's full of Acceptance/ Nonacceptance beats.
Present in that conversation is also this idea that Sherlock finds "real people" dull. This echoes something he said earlier, during the Pink Lady scene: "Dear God, what is it like in your funny little brains? It must be so boring." This seems related to acceptance or nonacceptance.
Alright, for the sake of argument, let's interpret Acceptance as Sherlock's drive is to be tolerated. He wants to be accepted into the investigation. When the police are being non-accepting of him, like at the very beginning, Sherlock's drive toward solving the suicides is pretty minimal. He's a bit of a pest during the press conference, but otherwise, he's out doing his own thing, looking into crimes where his help has been accepted, conducting experiments, and looking for a flat mate.
Once the police invite him in, Sherlock's drive skyrockets, and the more allowances are made for him, the more driven he becomes, until by the end of the Pink Lady scene, he's charging off to look for the suitcase by himself and ordering the police around and telling them what to do.
Note also that when the police first show up at the apartment to ask for help, Sherlock asks Lestrade who's on forensics, and when Lestrade says it's Anderson, Sherlock balks, his motivation momentarily waning because Anderson won't work with him (Nonacceptance).
In the end, this doesn't appear to be a story where the IC's inequity, whatever exactly Sherlock's is, get's resolved. In that case we don't necessarily expect to see his Solution strongly applied. As far as I know, that's not required.
In terms of how these things effect Watson, it's definitely his acceptance of Sherlock and Sherlock's invitations to come along on various aspects of the case that facilitates Sherlock's continued influence.
Sergeant Donovan warns Watson to stay away from Sherlock (Nonacceptance), and if Watson heeded her advice, the root of Sherlock's influence would evaporate.
I'm not sure if any of this is using quite the right approach. Dramatica has this to say about the IC's Problem element:
The Impact Character's Problem is the root of his impact as well, so whatever your story explores in terms of your Impact Character will have a tinge of this item to it.
That, at least, seems to be true of Acceptance.