I think it's going to turn out to be a Buccaneer ability that will have some similarities to CoC.
I made a post earlier this week on this thought pattern but there are basically three almost extinct ancient races in the series, the Lunarians, the Buccaneers and the Three Eye Tribe and each of their characteristic abilities are very similar to the 3 branches of Haki.
King's Invulnerability is akin to full body armament
Pudding's extraordinary conginitive abilities are similar to observation (i.e. not only was she able to see Sanji move on WCI when he save Chiffon, she can have access to VOAT when she awakens her 3rd eye)
and now Kuma's abilities seem to emphasize will power which is similar to conqueror's haki.
Now even though PoL and Conquerors Haki are somewhat similar in the sense that they are both will power based.
All it's applications so far have been based off of "protection":
Sanji "protecting" Nami from S-Shark and projecting his wil as an immovable barrier
Sanji "protecting" Bonney from Kizaru and projecting his will as a kick that can interfere with and destory light
Kuma "protecting" Bonney from the Celestials and projecting his will on his will-less body even though it had been taken from him.
Then there's Conquerors' haki which is based off "domination"
Conqueror's project their wills to dominate those weaker than them.
Conqueror's project their wills to amp up their abiliities.
So I can see Oda justifying PoL as a similar yet different way of projecting one's will power that is most likely characteristic to the Buccaneers.
Even though Sanji has kingly traits, he's more akin to "Kuma" who's more a of a "sefless" king as opposed to a "Judge" for instance who is more of a "conquering" king. Btw I'm aware that not everybody with conquerors haki wants to conquer something. Oda's not very consistent with that but I can legit see Oda giving Sanji something similar but yet distinct from Conqueror's haki via PoL.
Sanji is not really a character that wants to dominate others and this is emphasized by his backstory with his family so I can see Oda not wanting to give him CoC which is an ability that is based on "dominating" others. It is literally in the name
覇(dominate)王色 so maybe PoL is more of like a
守護(guard)王色 so "Color of the Guardian King" as opposed to "Color of the Conquering King"