The issue with CoC is that Oda has to give it to him now, because other wise he will have to rush it, like he did with Zoro, which writing wise isn't great considering how long it took for Luffy.
Let's look at Luffy:
Luffy unlocked it Pre-TS -> Trained for 2 years to learn to controll it -> unlocked the advanced version by seing it from Kaidou (he got it way too quick and easy here imo, considering how ''special'' it is supposed to be)
Luffy got a pretty long way from unlocking it to AdvCoC, which was always an issue when speculating when and if another SH is gonna get CoC, they would be able to learn it much faster in order for it to matter. Which is how it also turned out with Zoro and probably will also with Sanji.
Zoro:
Apparently used with Ashura against Kaidou -> Activated and used CoC + AdvCoC against King thanks to Enma ''pulling it out'' for him.
With Enma Oda took a short cut and could make Zoro skip the learning part about controlling CoC and go straight to AdvCoC (which i personaly never liked, because Enma already felt like a deus ex machina before that with the whole magical AP Boost, but whatever, it is what it is).
Sanji:
So in order for Sanji to get CoC and AdvCoC and learn how to controll it before the end game, we would probably need some sort of short cut aswell. And here is the problem, i don't see any. Sanji is not gonna get an Enma equivalent that would pull the CoC out of him.
I have thought that maybe the Germa and losing the emotions would play some part in it, maybe something like - Sanji losses his emotions and in order to get controll over them he would need CoC and basicaly to conquer his emotions and maybe even bring out the AdvCoC with it.
That is the only option i see and it's a little of a stretch.
Here is how i see it:
If Sanji doesn't get a short cut like Zoro, then Sanji would need to get basic CoC NOW!
Because this way he would have time to learn to controll it (even tho stil faster than Luffy, but at this point in the story that is to be expected) and then in a hard battle unlock AdvCoC as a PU.
Basic CoC:
Oda missed the perfect chance for Sanji to unlock it back in WCI, when his family was about to be exectued, he should have unlocked CoC, knock the fodder around them out and then break the Candy like he did. But Oda decided to go for a perfectly timed BM scream....
That would have been similar to how Luffy unlocked it.
Now you might say he didn't care enough about them, but he cared enough to not let them die and Reiju was there who he cared about alot.
And now is the question, what would bring out bigger emotions for him to overshadow that and let him unlock it. Nami or some other SH? It would feel kinda forced if all of a sudden an emotional trigger would work, when before it didn't.
AdvCoC:
AdvCoC is a PU, that means Sanji would need to fight someone where he would need this kind off PU.
And i don't see it on Elbaf. The Holy Knights are not gonna be so strong that Sanji would need such a PU to beat them - for that they would need to be way above YC level and i don't see it (outside of Shamrock obviously, but he wouldn't be Sanji's opponent).
Conclusion:
Either Sanji gets a short cut via Germa/Emotionals or something or he has to unlock basic CoC and work his way up to AdvCoC.
I do think that Sanji should get CoC - every Top Tier should have - and not some ''weird or special'' equivalent of it.