Other than just Kingly ambitions, the other problem i have is that it seems that Oda is going the non-haki route for Sanji with the Raid Suit, Germa Genes and now possibly Lunarian bloodline.
If you look at the people who do have CoC Haki, the vast majority of them actually have all 3. The only exception right now is Kidd who has only show CoC and no CoA or CoO, but like with Ace Oda may reveal that in another Data Book later down the road.
Haki/Haoshoku Haki | One Piece Wiki | Fandom
Sanji's only really proficient in CoO, his CoA is pretty average, which is why Oda gave him all the other stuff with the raid suit, germa genes and now the new bloodline thing.
If Oda is fore going Sanji's CoA, then it doesn't seem likely to me that Sanji will be getting CoC any time soon or in this Arc, when Oda has never given Sanji the Haki focus-whether its for CoA or CoO, let alone for CoC.