The plot implications are quite significant. For starters, it could change Naruto's relationships with his friends. Some might be jealous or afraid of his new power. Also, it could attract the attention of dangerous enemies. Those who were after Shisui or the Sharingan might target Naruto. This would put Naruto in a whole new set of dangerous situations and force him to grow and adapt in different ways. Additionally, it might also change the way Naruto approaches his ninja training, as he has to learn to master the Sharingan's abilities.
In the fanfiction, if Naruto gets Sharingan from Shisui, there are several plot implications. It might lead to a shift in the power balance in the ninja world. With Naruto's existing strength and the addition of the Sharingan, other villages might view Konoha as an even greater threat. This could spark new conflicts or alliances. Also, within Konoha, there could be political unrest. The elders might be worried about Naruto's new power and try to control or suppress him. And Naruto himself would have to deal with the internal struggle of being a Jinchuriki and now having an Uchiha power, which could be a major part of the plot's development.