I think Sanji should just awaken FS and basic CoC, while getting ACoC later.
This chapter seems to hint more towards FS than ACoC, as Iva's words and Sanji's resolve seem to be towards him not getting hit. He could and probably will get CoC in the process. But I do tbh see an issue with him going from no-CoC to ACoC. I mean yeah, Zoro did it, but he also had enma.
For the first 1000+ chapters of the story, we were introduced to numerous basic CoC users with no ACoC. Luffy, Chinjao, Doffy, Kata, and Kid. ACoC is a very hard ability to get, even if you already have basic CoC. It would just seem very convenient for Sanji to get it now all of a sudden.
With FS, Killingham wouldn't be able to touch Sanji. Sanji could effortlessly hack him to pieces. He could grab Killingham's head and go throw it into the ocean. CoC just might not be necessary at that point. Alternatively maybe it will be a loki type situation where Sanji unconsciously uses ACoC to shatter Killingham's heart.
In any case, I don't think Sanji masters ACoC this arc. He masters CoO and gets some CoC power on top, but that is something Oda will deal with later.