One idea could be exploring Naruto's relationship with his father in more depth. Maybe Naruto discovers some hidden jutsu that his father was working on before he passed away. Another could be about Naruto and Hinata raising their kids and the challenges they face as a family in a post - war Konoha.
In a 'Naruto and his family fanfiction', a great plot could be Naruto teaching his son how to control the Nine - Tails' chakra. It could show the bond between father and son, and also how Naruto passes on his knowledge and experiences. There could also be a sub - plot about Hinata being worried about their son's safety during the training, which would add some family drama to the story.
Well, a plot could revolve around Naruto's family tree. What if there were some long - lost relatives that suddenly showed up? It would be interesting to see how Naruto and his family dealt with that. Or perhaps a story where Naruto's family gets transported to a different dimension and they have to find their way back while facing new and strange threats.