One Piece theory suggests that Luffy’s imprisonment could help the Straw Hats in getting a power-up.

SUMMARY

The Straw Hat Pirates and Luffy are finding it harder and harder to beat their adversaries as the Egghead Island plotline progresses.
They desperately need some outside assistance or a power-up to let them escape the island while simultaneously defeating the Five Elders.
There is one theory that lays the groundwork for the crew to gain new abilities, but Luffy must first be captured.

As the story of the Egghead Island arc moves forward, it is getting more and more difficult for the Straw Hat Pirates and Luffy to defeat their enemies and escape from the island to the next phase of their adventure. Even with the help of the Giants, Dr. Vegapunk, and the Iron Giant, the Straw Hat crew is unable to fight against the Five Elders.

One Piece – Egghead Island | Toei Animation
They desperately need some external help or some kind of power-up that could aid them in not only escaping from the island but also defeating the Five Elders for good. However, as of now, there is not much hope for the Straw Hat Pirates. While there are theories about Luffy getting a power-up, it won’t be sufficient to fight against all of the Five Elders.

The only possible way for the Straw Hat crew to win against the forces of the World Government and the Navy is for every member of the crew to get a second power-up, similar to the one after the time skip. And there is one theory that sets the perfect plot for the crew to get new abilities, but for that, Luffy needs to be captured.

One Piece Theory Predicts Luffy Might Be Left Behind

According to a theory posted by u/harlojones on Reddit, the next few chapters of the Egghead Island arc could be the last of the narrative, and they would hint at the Straw Hat Pirates escaping and sailing toward Elbaf along with the giants, but they might have to leave Luffy behind as he is the only one who is somewhat capable of dealing with the Five Elders.
Although his power is not enough, he could stop them from going after his crew, who are the most important to him. If given the choice, Luffy would gladly sacrifice his freedom for the crew, and this would make an important narrative of the story. Also, the Five Elders might be satisfied with capturing the newly declared Yonko of the Sea.

Luffy Fighting One of the Five Elders | Viz Media
The theory also states that Luffy would be captured by the Five Elders and imprisoned in the same cold place where Imu has kept Joy Boy’s straw hat. This is because rubber loses its elasticity and becomes brittle, thus weakening Luffy’s powers. Also, it would motivate the rest of the Straw Hat crew to power up and rescue their captain.

The Straw Hat Pirates May Be Getting a Second Power-Up

The main component of the One Piece theory is that Luffy’s capture will force the crew to get a power-up, and the best place for them to enhance their abilities will be Elbaf. There is a chance that the crew might learn the entire mystery of Joy Boy and Nika on Elbaf and their connection to Luffy. Also, they can possibly meet the Red-Haired Pirates.
Elbaf Village in One Piece | Toei Animation
They can train under Shanks and his crew and learn to unlock new abilities that will make them stronger for the final battle. A second power-up in the final phase of the One Piece story could be a perfect plot line for every member of the crew. It would also create a bond between the Straw Hat Pirates and Shanks’ crew.

The theory also states that the crew could call the Grand Fleet, which would aid them in launching an attack on the World Government and saving their captain. This could be the perfect rendition of the final war, and other organizations, such as the Revolutionary Army, could join the war and help the crew save Luffy.