Well, he might see some amazing technological advancements. Maybe flying cars are everywhere and houses can move. He could also meet his descendants and see how his family has grown over the years.
In this fanfiction, James Potter could face a future where magic has evolved in unexpected ways. There could be new spells and magical creatures. He might also get involved in some sort of future conflict that threatens the wizarding world and have to use his old - school magic skills to help. He could be shocked to find that some of the values in the wizarding world have changed drastically too.
Perhaps in 'James Potter goes to the Future' fanfiction, James discovers that the future wizarding world has made great strides in inter - magical species relations. He could encounter half - human, half - magical - creature hybrids living among wizards and witches without any discrimination. Also, he may find that Hogwarts has been updated with new magical defenses and teaching methods. He would surely be amazed by the new potions and charms that have been developed.