After escaping from Big Mom’s territory, it was later revealed that Germa 66 had created a Raid Suit specifically designed for Sanji to use, which was secretly hidden and given to him as a parting gift during the Vinsmokes’ assistance in his and Luffy’s escape from Cacao Island.
Sanji is annoyed at Niji for giving him a raid suit in secret, seemingly mocking him for his lack of strength right until the very end. Luffy and Chopper are trying to convince him to keep it. Sanji claims that he doesn’t need science to make himself stronger leaving it in the hands of the rest of the crew, who have chosen to hold onto the item just in case.
Sanji is going to be forced to throw away his pride in order to become stronger, just like Zoro did.
When Zoro was desperate and struggling, he had to throw away his pride and beg his biggest rival to become his master. He ignored his pride as a samurai in order to protect the crew and be useful for Luffy.
Now Sanji is going to be forced to make a similar sacrifice, enbracing the family that he despises so much and using the raid suit. Once he comes to terms with his origins as a Vinsmoke, I think he’ll be able to grow as a character and become even stronger.
I think the raid suit will actually further increase Sanji’s already-monstrous speed to the point where he could go up vs a Yonko Commander or even a Marine Admiral.
Sanji could very well end up becoming the fastest non-DevilFruit user in the series, giving him the demon-speed edge of potentially going toe-to-toe against (hopefully) Kizaru, another speed-demon, in the Great War.
*Theory by FlyingRodentMan/brazilianfreak