The final move of Gear Fourth: Model Snakeman will be for Luffy to unhinge his jaw and eat Katakuri whole.

In subsequent chapters, Luffy won't get his usual post-meal fat belly, but rather, a lump larger than his body which starts in his neck in the scene after he wins.

In the subsequent scene, it will be slightly smaller and in his shoulders.

In the scene after, smaller still and in his torso.

When they arrive at Wano, Luffy will then reveal the secret technique of snakeman: molting. He will shed his skin and the new Luffy will emerge: he looks just like current Luffy but a bit older, and Garp's height.

Luffy will defeat Katakuri by simply eating him when he turns into mochi.

Big Mom's flashback will reveal that she is, in fact, Luffy's sister.

@caesar:

I don't think that will happen.

I think you're confused about what thread you're in.

Speaking of which, another prediction: Sanji's face will remain permanently swollen/deformed, in a mirror of his own Parage Shot.

The conflict with Big Mom will be resolved with a Davy Back fight, which will result in the Strawhats gaining the following crew members from Big Mom's crew: Sanji, Jinbe, and Big Mom herself.

Big Mom will then end up sacrificing herself to save the crew from Kaido.

Cracker will end up landing in the ocean and crash into Jack, forming Crackerjack. For the rest of the series, we'll periodically get random panels of Crackerjack sitting at the bottom of the ocean, looking displeased.

The final scene of One Piece that Oda has envisioned from the beginning involves Luffy dying from an allergic reaction to a bee sting from a perfectly normal bee.

It will echo Kuina's death, and drive home the point that even the strongest people can die from a random accident.

Luffy will end up eating the entire island.

And be "island", I obviously mean Fishman Island.

Sanji will unlock his dormant genetic modifications thanks to being hypnotized by Jango after it is revealed that Hina was one of the guests invited to the tea party/wedding.

Blackbeard will acquire three additional Titan Captains, named "Harder", "Better", and "Faster".