I think it's pretty far-fetched. The Rinnegan is not something Naruto would typically obtain, especially in a Narusaku context. It could make the story less believable and stray too far from the original canon.
His relationships would change too. Some of his friends might be a bit intimidated by his new power at first. But Naruto would work hard to show them that he's still the same person. He could also form new alliances with those who are interested in the Rinnegan's power, either for good or bad reasons. Overall, he would grow into a more complex and powerful version of himself, with a greater sense of responsibility for the ninja world.
Another possibility is that it's a result of some strange chakra experiment gone wrong (or right). Scientists in the Naruto universe are always dabbling in chakra research. Maybe an experiment meant to enhance her natural abilities instead gives her the Rinnegan, and she then has to learn to control it quickly to avoid being consumed by its power.
You can find 'Naruto Shippuden Narusaku fanfic' on some popular fanfic websites like Fanfiction.net. There are a large number of Naruto - related fanfics on this site, and you can easily search for Narusaku ones. Another option is Archive of Our Own (AO3). It has a great collection of fanfics, and you can filter your search specifically for Narusaku fanfics within the Naruto Shippuden category.
You can try looking on fanfic websites such as FanFiction.net or Archive of Our Own (AO3). These platforms have a large collection of fanfictions, and there's a good chance you'll find 'narusaku naruto returns fanfic' there.
In fanfiction, the idea of Naruto having the Sharingan and Rinnegan is often a creative and out - of - the - box concept. It could be due to some kind of powerful jutsu or a unique plot device. Maybe a powerful enemy uses a forbidden jutsu that somehow transfers the powers to Naruto. Another possibility is that in an alternate universe created by the fanfic writer, the rules of chakra and kekkei genkai are different, allowing Naruto to possess these powers.
One popular fanfic could be where Naruto gets the Rinnegan through some kind of ancient power transfer. In this fic, he might use the Rinnegan's powers in unique ways, like combining its abilities with his own Sage Mode and Nine - Tails chakra. This could lead to him being able to perform new jutsu that are a blend of different powers.
One interesting fanfiction could be where Naruto gets the Rinnegan and uses it to bring a new era of peace in the ninja world. He might use its powers to understand the true nature of chakra better and teach others. Another could be a story where Naruto has the Rinnegan and teams up with Sasuke in a whole new way, combining their powers in unexpected and powerful combinations.
His relationship with Sasuke would likely become more complex. Sasuke might be both jealous and intrigued by Naruto's new powers. Naruto would have to prove that he still values their friendship despite his increased strength. With Sakura, she might see Naruto in a new light, perhaps with a bit more admiration as he now has such rare and powerful abilities.
In many Narusaku fanfics, Naruto might bring Sasuke back through the power of their friendship. Naruto's unwavering belief in Sasuke could be a key factor. He may constantly remind Sasuke of their past together, the bonds they formed as teammates in Team 7. For example, Naruto could recall the times they trained together, their shared dreams, and how they protected each other in battles. This could slowly chip away at Sasuke's resolve to stay away and eventually lead him to come back.
His relationship with Sasuke would likely be very different. Since Sasuke has also had experiences with the Rinnegan, they might now have a new level of understanding between them. They could train together to master the powers of the Rinnegan or compare notes on how to use its abilities.