Well, Naruto could show Boruto his Sage Mode power. Sage Mode gives Naruto enhanced strength, speed, and the ability to sense chakra more acutely. It's a very powerful form that Naruto has mastered over time. By revealing it to Boruto, he might be teaching Boruto about the different levels of power and the hard work required to achieve such power.
It could also be that Naruto sees in Boruto's eye a sign of an emerging danger. The eye might hold a clue to a new enemy or a brewing conflict. Naruto, being the experienced ninja he is, would then start to take precautions and train Boruto more intensively to face whatever this sign in his eye indicates.
Another reason could be related to his personal growth. He might be trying to master the power of the eye in private. Naruto has always been one to face challenges alone at first. By hiding his eye, he can focus on understanding and using its power without distractions or the pressure of others' expectations.
One consequence could be that his friends might start to suspect him. Since Naruto is usually an open book, hiding something as significant as his eye could make them wonder what he's up to.
Well, it could be due to a powerful enemy attack during a fight in Wave. Maybe an enemy with a sharp weapon or some dangerous jutsu managed to strike Naruto's eye.
He might show his scars to Sasuke. Given their complex relationship, it could be a powerful moment between them, a way to show Sasuke that Naruto has also faced great pain in their separation and the events that followed.
One possible consequence could be a change in his fighting style. Without his eye, he might have to rely more on his other senses like hearing and smell, similar to how blind ninja in the Naruto universe adapt. For example, he could focus more on using his chakra to sense the movements of his opponents.
In the context of fanfiction, it might also be a plot device to explore Naruto's vulnerability. It could lead to new character developments, such as others seeing him in a new light. Maybe it causes some characters to re - evaluate their relationship with him, while for others it could be a source of inspiration, seeing that even someone as strong as Naruto has his own set of hardships.