One possible plot twist could be that Naruto sees a future where his friends turn against him. This would shatter his world as he values his friendships deeply. He might then struggle to figure out what went wrong in the future and try to prevent it in the present.
In the fanfiction, Naruto might see a future where he fails to become Hokage. This would be a huge blow to him. However, instead of being discouraged, he could use this vision to learn from his future mistakes, work on his weaknesses, and strive even harder to achieve his dream.
Perhaps he sees a future where Konoha is destroyed. This would drive him to take extreme measures in the present to avoid such a catastrophe. He could start training harder, form new alliances, or even try to change the political situation in the village to ensure its safety.
In this fanfiction, Naruto might look into the future and find out that the new generation of ninjas has lost their way. They no longer value the things he fought for, like friendship and hard work. So, he has to come up with a plan to inspire them again. He could start by sharing his own experiences and showing them the importance of the ninja way.
Another plot twist might be that Naruto reads a future where the entire ninja world is in ruins. This could lead him to take extreme measures in the present to prevent that future from happening. He might try to unite all the ninja villages in a way that has never been done before, facing many obstacles along the way as different villages have their own interests and grudges.
One possible plot twist could be that Naruto's love for Kakashi from the past disrupts the timeline. Maybe his feelings cause him to unknowingly change events that were supposed to happen. For example, he might prevent Kakashi from making a certain decision that was crucial in the original timeline.
Obviously, Naruto himself is the most affected as he has to deal with the knowledge of the future. But his friends like Sasuke, Sakura, and Kakashi would also be deeply affected. If Naruto saw a future where Sasuke was in trouble, he would do everything to change it, which would impact Sasuke's life. Sakura, being Naruto's teammate and also caring about Sasuke, would be involved in any plan Naruto made. And Kakashi, as their sensei, would be there to guide and support them through the changes Naruto tries to make based on his future vision.
A plot twist could be that they see Naruto losing his way. This would be a huge shock for them as they always believed in Naruto's goodness. But then, as the story unfolds, Naruto finds his way back due to a memory or a message from his parents that he somehow receives in a moment of crisis.
One common plot twist could be that Naruto sees a future where his friends turn against him, but then discovers it was an illusion created by a new enemy. Another might be that he sees a future where Konoha is destroyed and has to find a way to change that fate. Maybe he sees a future where he becomes a villain himself and has to struggle to prevent that from happening.
One of the most interesting plot twists could be that Naruto discovers a new form of chakra that has the power to rewrite history. This would completely change the power dynamics in the Naruto universe.
One idea could be Naruto seeing a future where the Hidden Leaf Village is in ruins due to a new, powerful enemy. He then spends his present time training harder and forging new alliances to prevent this future. Another plot could involve him seeing his friends in danger in the future, so he starts to teach them new jutsus in the present to better protect themselves.
In a Naruto is Vergil fanfiction, it could be that Naruto's connection to Vergil is through a dream - like realm. Every time Naruto sleeps, he enters a world where he meets Vergil and learns from him. Over time, Naruto starts to incorporate Vergil's values into his own. He becomes more focused on power for the sake of protecting those he loves in a more 'Vergil - esque' way, which means he might be willing to make some sacrifices that he wouldn't have considered before, like sacrificing some of his own personal relationships for the greater good of the village.
In 'naruto in the future fanfiction', perhaps Naruto has passed on his ninja way to a new generation. His son or disciple could be facing a new threat that combines old and new jutsu. Maybe they have to deal with a group that has found a way to use ancient, dark jutsu in a modern, technological world.