The talk about a character having Conqueror's Haki in One Piece is always a controversy, given how only a few have awakened this overpowered ability. However, as Zoro and Luffy have awakened it, and Sanji is a part of the monster trio, it would make sense for the Black Leg to awaken Conqueror's Haki. Moreover, what better time to do so than the final saga?
The appearance of Scopper Gaban strengthened the lore about love being powerful enough to contradict logic. Moreover, Sanji's acts in the Egghead Arc also proved that love might also be a force that could give devil fruits a run for their money.
So, Sanji might awaken Conqueror's Haki in the Elbaph Arc, and what other opponent to awaken it against other than Saint Sommers, who has a contradictory meaning for love.
Disclaimer: This article contains potential spoilers from the manga series and expresses the author's opinion.
Exploring why Sanji might awaken Conqueror's Haki in One Piece's Elbaph Arc

Conqueror's Haki is one of the three types of Haki in One Piece that only the strongest awaken. Unlike other Haki types (Armament and Observation), this type cannot be awakened through training and is present in individuals since birth. Characters like Monkey D Luffy, Shanks, Whitebeards, and others have awakened this Haki solely due to their natures as conquerors.
However, one character has been speculated to awaken this kind of Haki since the early days, and the only thing holding him back is his obsession with love. That character is the Straw Hat Pirates' cook and the right-hand man of Monkey D Luffy, Vinsmoke Sanji.

Vinsmoke Sanji is one of the strongest One Piece characters who doesn't have a devil fruit. A part of his strength comes from his obsession with love. Moreover, this 'obsession with love' is also the biggest factor as to why the fans think Sanji might never awaken Conqueror's Haki. However, this factor might be the deciding factor to Sanji awakening this type of Haki, and the final saga proves it.
During the One Piece's Egghead Arc, Sanji's power of love has defied logic numerous times. For instance, during a clash with Admiral Kizaru, Sanji diverted the Admiral's attack, claiming that this was due to his power of love. Moreover, before this incident, Sanji did the same with S-Shark, hinting that his power of love might have the potential to do more than just talk.
During the One Piece's Elbaph Arc, Scopper Gaban made his first appearance, and he shared Sanji's 'obsession with love.' Given Gaban's potential as one of the strongest ones on the Grand Line, Sanji might also be destined for greatness, and this could only be possible through the awakening of Conqueror's Haki.

However, whom could Sanji awaken it against? Saint Sommers is one of the newly introduced Holy Knights, and the most intriguing thing about him is his concept of love.
Unlike Sanji, whose concept of love is wholesome, Saint Sommers' is the exact opposite. Sommers considers hurting as the true form of love, making him Sanji's destined opponent. So, in a combat, Sanji might get infuriated over Saint Sommers' concept of love, and this might be the point where the Black Leg would awaken his Conqueror's Haki.
Analysis and final thoughts
Eiichiro Oda has depicted awakened power-ups as hilarious numerous times, including how Nami could overpower Luffy, one of the strongest pirates on the Grand Line, in her rage. So, Sanji awakening Conqueror's Haki in his rage over Saint Sommers' concept of love might be logical.
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