Another plot twist could be that an enemy uses their relationship against them. The enemy could spread rumors or false information to create chaos and turn the ninja world against them. Naruto and Sasuke would then have to fight not only to protect their relationship but also to clear their names and prove that their love doesn't mean harm to the ninja world.
One possible plot twist could be that they are being secretly manipulated by an unknown enemy who wants them out of Konoha for some dark purpose. Maybe this enemy has spread false rumors about them in the village, making them feel like they have no choice but to leave. Another plot twist might be that they discover a long - hidden truth about their families that is connected to some ancient power outside of Konoha, which compels them to leave in search of answers.
One possible plot twist could be that Naruto and Sasuke join Akatsuki with the secret intention of reforming it from within. They might want to change the organization's goals from causing chaos to actually protecting the shinobi world in a different way. For example, they could try to use Akatsuki's resources and manpower to fight against a greater threat that the traditional shinobi villages are ignoring.
A plot twist could be related to Yugito's tailed beast. Maybe the power of the two - Naruto's Nine - Tails and Yugito's Two - Tails - has some unforeseen consequences when they get married. It could attract the wrong kind of attention from those who seek to use tailed - beast power for evil. Or perhaps the tailed beasts themselves have some sort of reaction to their union that changes the relationship between Naruto and Yugito, like they start to communicate with each other in a new and strange way through the beasts.
It could be that Fem Sasuke is under some sort of mind - control when she kidnaps Naruto. A powerful enemy, like Orochimaru or a new villain, might have used a jutsu to make her do this. As the story progresses, Naruto would then have to find a way to break the mind - control on Fem Sasuke while also dealing with the situation of being kidnapped.
The curse mark could have a mind of its own. It starts to communicate with Naruto and Sasuke in their dreams, trying to manipulate them into doing its bidding. Naruto, being the optimistic one, tries to resist and turn the curse mark's power into something positive. Sasuke, however, is more tempted by the power it offers. This could lead to a rift between them as they have different approaches to dealing with the curse mark, and their relationship would be put to the test.
One possible plot twist could be that they face opposition from their respective clans who still hold grudges from the past. The Uchiha clan might not accept Naruto easily due to his connection to the Nine - Tails. Another twist could be that Sasuke discovers a new power within herself during their marriage that has unforeseen consequences for the village. Maybe it attracts enemies who want to steal that power.
One possible plot twist could be that Naruto, upon getting Sasuke's Rinnegan, starts to see visions of the past and future of the Uchiha clan. This new power might make him question his own beliefs and the relationship between the Senju and Uchiha. He could see the events that led to Sasuke's decision to give him the Rinnegan and struggle with the responsibility that comes with this powerful dojutsu.
A plot twist could be that Sakura and Hinata actually team up against Naruto in some way. Perhaps they realize that Naruto is being pushed into a relationship by the village elders for political reasons. So, they decide to fake a relationship between themselves to make Naruto see that he should be free to choose his own path and not be pressured into a marriage. This would turn the typical love triangle on its head.
One possible plot twist could be that their families oppose the marriage at first. Maybe Ranma's father has some old feud with Ryoga's family that they need to overcome. Another twist could be that a third character, who has feelings for either Ranma or Ryoga, tries to break them up. For example, Akane might realize she still has feelings for Ranma and tries to stop the wedding.
One possible plot twist could be that Gaston has a change of heart and realizes the error of his ways. He starts to see Belle not just as a trophy to be won, but as a person with her own dreams and desires. This newfound understanding could lead to a more complex relationship where he tries to make amends for his past behavior and truly win her heart in a more honorable way.