When the Marauders travel to the future in a fanfiction, they may meet the students of Hogwarts in that future time. These students could be very different from the ones they knew in their own time. The Marauders might also come across future wizards and witches who are experts in new areas of magic that the Marauders have never even heard of. Additionally, they could meet people who are working on projects to preserve the history of the wizarding world, and these people might be very excited to meet the Marauders who are a significant part of that history.
Obviously, the Marauders themselves - James Potter, Sirius Black, Remus Lupin and Peter Pettigrew would be the main characters. They are the ones 'meeting' the future after all.
In this fanfiction, it could be that the future has a new Dark Lord. The Marauders are brought forward in time to stop this new threat. They face challenges like understanding the new forms of magic and technology that the future Dark Lord has harnessed. They also have to deal with the fact that the future wizarding world has different social and political structures. They might start by infiltrating the Dark Lord's lair using their Marauder's Map - like skills, but find that the map doesn't work as well in the future, leading to all sorts of interesting and dangerous situations.
The marauders would probably have to adapt their way of thinking. In the future, the concepts of right and wrong, good and bad might have shifted. They'd need to understand these new perspectives to fit in.
They might be shocked by the advanced technology. For example, seeing flying cars and instant communication devices everywhere could leave them in awe.
One possible plot could be that the Marauders use a time - turning device by accident and end up in the future. They might be shocked by the advanced technology and different social norms. They could also meet their descendants or versions of themselves that are very different from what they expected.
He could meet his future self. This would be a very interesting encounter as he could learn from his future self about what he has accomplished and what mistakes he should avoid. He might also meet the future generations of his family, like his grandchildren or great - grandchildren.
There's a chance he could meet an older and wiser Kakashi. Kakashi might have new insights and stories to share with Naruto from all the years that have passed. And also, he could run into future shinobi who look up to him as a legend from the past.
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.
Anakin could encounter future versions of his friends or enemies from the past. For instance, he could run into a future version of Obi - Wan Kenobi who has also somehow traveled to that future time. Or perhaps he meets a new generation of Sith who have different motives and methods compared to the Sith he knew in his own time. They could challenge his understanding of the dark side and the Force in general.
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.