Goten could meet the younger versions of his friends like Krillin or Yamcha. They might be a bit skeptical of him at first. He could also run into Master Roshi, who would probably be interested in Goten's abilities and might try to teach him some old - school techniques. And there's a chance he meets Bulma, who could be intrigued by his futuristic knowledge and might even try to get some tech ideas from him.
In the past, Goten may come across villains that his family has fought before. For instance, he could meet Raditz. This encounter would be intense as Raditz was a powerful foe. Goten would have to be careful as Raditz might not take kindly to this strange boy interfering in his plans. Or he could meet Frieza's minions, which would also pose a threat to him and potentially change the course of history if he's not careful.
He might accidentally change the future. For example, he could prevent important events from occurring that were crucial for the development of the present he came from. Maybe he meets his parents at a younger age and reveals too much about the future, which could cause them to make different decisions.
Naruto would meet his younger self. This would be a really strange situation. He could also meet all the important shinobi from the past. For example, the First and Second Hokage. He might have a chance to learn from them directly, instead of just hearing about them in stories. Additionally, he could meet some of the characters who were only mentioned in passing in the original story but had a big influence in the past.
In the past, Sakura could meet the original creators of the magic system she uses. They might be able to teach her things that have been lost over time. She may also encounter a young, talented artist or inventor who was never mentioned in the history books. This person could be creating something that will have a big impact in the future. And there's always the possibility that she meets a kind - hearted stranger who becomes her best friend in the past and has a lasting impact on her life, even when she returns to her own time.
They could meet past Air Nomads. These could be great benders or spiritual leaders who can offer wisdom and advice.
She could meet her future self. This would be an interesting encounter as they could compare their experiences and knowledge. Her future self might give her some advice on things she should do or avoid in her own time. Another person she could meet is a descendant of her friends. For example, a grandchild of Harry and Ginny who has inherited their bravery and magical skills.
One idea could be that Sarada travels back in time and initially mistakes Naruto for Sasuke. This could lead to some humorous misunderstandings as she tries to interact with him. For example, she might challenge him to a fight thinking he's Sasuke, only to be completely surprised by Naruto's different fighting style and personality.
He might meet the future versions of Naruto and Sakura. Their relationship with him could be very different in the future, perhaps they are now leaders of the village and Sasuke has to adjust to their new status.
He could meet his future self. It would be an interesting encounter as he could learn from his future experiences and wisdom. Or he might meet people who have studied his past adventures and see himself through their eyes.
He could meet his future self. His future self might be wiser, having learned from all the experiences in the past. They could have a deep conversation about Shinji's purpose and the mistakes he's made.
Naruto may run into some friendly space explorers who are amazed by his ninja skills. They could help him navigate the strange new world of space and introduce him to advanced technologies that are different from what he's used to in the Hidden Leaf Village. There might also be some wise, old beings in space who can teach Naruto new ways to master his chakra.