The central story feature of One Piece Odyssey is time travel. This allows you to revisit beloved locations from the series with new spins and flavors. The Straw Hats have all the information, and characters get to play different roles. It's a shame then, that so few islands are revisited.
Only five of the several dozen islands that appear in the series were chosen for Odyssey. Given how different the islands were from their anime counterparts, it's fun to imagine what might have been for the other locations. If a sequel were to be made, these islands would be the first picks.
10 Drum Island
Drum Island is the first winter setting in the series, and it's home to Chopper, the beloved, reindeer doctor. This culminated in a truly beautiful arc with one of the most heartbreaking flashbacks to ever grace the series. Chopper deserves the world, and seeing him return home, even if for a moment, would be a start.
Drum Island's scenery can't be undersold either. Odyssey's art style brought the Venice-inspired Water 7 to life, and it would do wonders to Drum Island. The bloom of the massive Sakura tree aloft the snowcapped mountain would be enough to justify its inclusion.
9 Fishman Island
A few islands were sorely missed in Odyssey for their villains. Hody Jones qualifies, but not for the right reasons. Hody Jones may be one of the most punch-able faces in the series. He genuinely believes in his own hype, but he was getting KO'd by Luffy's second in command. Now? Usopp could probably ruin his life. He must be taught a lesson!
It would be a pleasure to see many of Fishman Island's inhabitants again. Princess Shirahoshi and her shark companion were a delight the first time around. This would give several crew members who didn't interact with Shirahoshi much a lot more time with her.
8 Skypiea
It makes sense why Skypiea isn't in One Piece Odyssey. The entire game is one long parody of it. Still, you never actually visit a true sky island in the game, and Skypiea would've given you that chance. A fluffy sea of clouds instead of the blue ocean would have been amazing to see animated.
The villain of the arc, Enel, would've been especially fun to defeat with the current powered-up Straw Hats. He was already a push over with Luffy, as a rubber man, being the natural counter to Enel, an electric man. If anything, it'd give you another look at the iconic "Enel face."
7 Sabaody Archipelago
If any island deserves to be rendered in Odyssey's art style, it's the Sabaody Archipelago. The entire island chain is populated by giant soap bubbles and massive trees. It's breathtaking and, understandably, a tourist trap in world.
The Straw Hats suffer a total defeat on Sabaody for the first time in the series, and it'd be interesting to see if they're powerful enough to avoid the same pitfall now. The encounter would be massively stacked in their favor, since it's a memory, but it's still fun to imagine beating on a Marine Admiral.
6 The Conomi Islands A.K.A. Arlong Park
Arlong Park may be a bit messy to replicate with all the modern Straw Hats, but it's antagonist simply must be punched again. So many One Piece villains are too likable in their villainy. It's easy to root for them. Arlong does not make that list. He is the series first hate-able villain, and it would be an honor to dismantle his syndicate again.
Returning to Nami's home island would give her agency she didn't have previously. Luffy had to save the island last time, but now Nami could be the one saving her friends and family. The addition of four extra crewmates would also tip the scales heavily in Nami's favor.
5 Reverse Mountain
The Straw Hats all have tragically devastating backstories. It's almost a prerequisite to be motivated by a dead loved one to join the crew. Brook the musician has the worst backstory — Laboon, a friendly whale, has been waiting for Brook's crew to return to him for 50 years. Now, Brook is the only one left.
Let Brook see Laboon again! It's almost guaranteed to happen in the series, but there could've been some fan service and maybe a small meeting with them in returning to Reverse Mountain. It's just a memory, but it'd be something. Laboon thinks Brook is dead, or worse, that he abandoned him. This must be rectified.
4 Baratie
Revisiting Baratie would be fun. Flat-out fun. It has one of the best gimmicks of any island, being a floating restaurant staffed entirely by a pirate-led crew of chefs. The lack of consequences in the memory means Luffy would probably try to eat them out of business. A minigame depicting such an act wouldn't be unappreciated.
Baratie features another villain who would be a treat to fight at the Straw Hat's current strength. Dracule Mihawk, the world's greatest swordsman, decimated Zoro in a dual last time. Chances are he'd still lose at this point, but through plot contrivances, you could best Mihawk for the first time in the series.
3 Whole Cake Island
Whole Cake Island is an island made of a whole cake. The scenery on this island would be spectacular. And delicious. It's a shame absolutely everyone on the island is an enemy. Whole Cake Island is the capital of one of the four emperors of the sea, and Luffy was out of his league attacking them on their home turf.
The lack of allies on the island would make the island heavily combat centric. Last time the Straw Hats were here, they were missing half of their crew. So, this time things would be vastly more in their favor. A mock fight against an emperor could rival the best bosses in the game.
2 Mary Geoise
Mary Geoise is a location not even the Straw Hats have visited yet. The series visited Mary Geoise during the Reverie arc where they were absent. This would give you a chance to see them wreak havoc by joining forces with The Revolutionary Army to assault the World Government's capital.
Sabo, Luffy's brother, was also a key figure of the Reverie, which would give Luffy another chance to interact with him. Fighting in the Reverie would allow for the first in-game appearance of Admiral Ryokugyu too, a character who's only appeared in the series once so far.
1 Wano
When Odyssey launched, Wano was the most recent arc in the series, and because of that it might've been logistically impossible for it to appear in the game. That might be for the best, however, as its inclusion could overshadow the rest of the game with its earth-shattering plot developments. Still, fighting two of the four emperors at once would be a power trip.
The art style of Wano is incredibly unique in the series, being inspired by Japanese Ukiyo-e paintings. Odyssey could flesh the style out in 3D to give you a deeper look at the locale. You could also interact with dozens of colorful side characters who'd been with the series for years.