Sanji bros already know my take on his potential powerups but will reiterate for the mandem.
With regards to CoC, aside from ① the apparent neccessity for Sanji to unlock CoC in order to be able to combat immortality, ② Sanji's direct parallel in the Roger pirates in Gaban having CoC, Oda's naming for Sanji Jambe powerup progression pattern is already hinting at it so there is a very strong possibility that he does get it
悪魔/Demon (Diable - Red Flames) → 魔神/High Class Demon (Ifrit - Blue Flames) ⇨ 魔王/Demon King (??? - Black Flames)
Black Flames in general has been something that has been speculated in the Sanji fanbase since time memorial and a PU he's almost guranteed to get. Only question is how that is going to come about. Some folks thing it's gonna be a direct result of him merging CoC with his Flames, whereas I'm personally more in the PoL camp (i.e. if there is an ability that is going to be able to conjure black flames which doesn't logically exist with the exception of a DF like Imu, it's going to be a bonkers ability PoL imo)
Then there's a potential demonic transformaiton for Sanji which I think could tie all of that together (.i.e this I think is going to be Sanji's peak in the same sense G5 is Luffy's). If you wanna know my extensive thoughts on this you can read this
thread (isn't long) but to summarize, some hints of a potential transformation for Sanji are;
① his gag demon transformations
② his devil related quotes as well as the naming of his Jambe powerups
③ Oda's been doing this ting narratively where he's been writing Luffy and Sanji as counter parallels, so my logic is that Sanji is going to have a transformation that mirror's Luffy's (i.e. for more details on this you can read the thread I linked in this post)
and now with the revelation of Imu's abilities, I feel like his existence further strengthens this theory. With the Sanji v Imu interaction it kinda felt like Oda was showing Sanji what he could potentially be going forward with Oda having Imu engaging Sanji with his fighting style and coating his kick in black flames. Also only noticed this after watching the reviews of the chapter but Imu has one of his eyes covered like Sanji does which I thought was interesting (i.e. btw I'm not saying Sanji is going to be as strong as Imu, but rather that Imu could potentially be a model of the direction Oda's going to go with Sanji)
But yh I went a bit of track there but getting back to original main discussion of the thread, if I'm on the money with regards to Sanji's Jambe powerups naming pattern then there's a strong likelihood that Sanji will awaken CoC with his next Jambe powerup which will almost certainly be Black Flames.
Also I wouldn't rule out Sanji potentially being able to use "maki" due to his devil connections but even if Oda ultimately doesn't go that direction, the revelation of "maki" can lead to the possibilty of different types of "Ki" exisiting in the series and PoL could potentially be another type.
So a lot of exiciting possibilities for Sanji going forward