On the positive side, some might see Naruto as a powerful asset. Since the Kyuubi is extremely powerful, if they believe Naruto is the Kyuubi, they could try to use his power for their own good. However, this also means they might not see Naruto as an individual with his own feelings and will. His relationships would become more about what he can do for others rather than true friendship.
Maybe it's because Naruto has some sort of special connection or resemblance to the Kyuubi that Kushina notices. For example, Naruto might display some of the Kyuubi's power characteristics in an obvious way that makes Kushina jump to that conclusion.
The Kyuubi often adds an element of mystery and power to Naruto. In fanfictions, this can translate into his relationship with Hinata in various ways. For example, the Kyuubi's power might be seen as something that makes Naruto more worthy of Hinata in the eyes of some characters in the story. Or, the Kyuubi could have a will of its own and actually push Naruto towards Hinata, seeing her as a good influence on Naruto. This can lead to some very unique and engaging story arcs within the fanfiction.
At first, Naruto might see the Kyuubi as just a source of power. But as he starts to protect it, he realizes it's more of a partner. Their relationship evolves from a simple user - power source dynamic to a deep - seated friendship. He begins to understand the Kyuubi's emotions and past, which further cements their bond.
In this fanfiction, their relationship becomes more of a partnership. Instead of Naruto just using the Kyuubi's power, they work together as brothers. Naruto might start to understand the Kyuubi's feelings and motives better.
Naruto might feel abandoned at first. Since Kushina is his mother, her leaving could make him feel lonely and question why she has to go. He may become more withdrawn.
It could add to the popularity of certain types of fanfiction. If Kushina is seen as being obsessed with it, more fans might be interested in exploring the fanfictions she might be interested in. For example, if there are fanfictions that focus on Kushina's relationship with Naruto in new ways, those might gain more attention.
In fanfiction, the Naruto - Kyuubi pairing can greatly expand the power dynamics. For example, they might be able to defeat stronger enemies together more easily. It can also change the relationships Naruto has with other characters. If he has a closer bond with the Kyuubi, some characters might be more in awe or more fearful of him.
Well, if Kushina becomes Naruto's servant in the fanfiction, it would drastically change the family dynamic. In the original Naruto story, Kushina is Naruto's mother. But in this fanfiction, Naruto would be in a position of power over his own mother. This could lead to some very interesting plot twists. For example, Naruto might struggle with the moral implications of having his mother serve him. It could also change how he views family relationships and his own identity. Maybe it would make him more confident in his leadership abilities since he has someone as important as Kushina under his 'command'.
This kind of fanfiction can have a negative impact on the Naruto fandom. It can make many fans feel disgusted because it distorts the important family relationship. It may also lead to division within the fandom, with some fans who support this kind of extreme and unethical creativity and those who firmly oppose it.
His friends might respect his decision more. They know how powerful the Kyuubi's chakra is, but also understand Naruto's reasons for not wanting to use it. This could strengthen their bond as they see Naruto's integrity.