Naruto could potentially gain the ability to access some of Madara's memories. This would give him knowledge about ancient ninja techniques and the history of the Uchiha clan. Also, he might be able to use Madara's space - time ninjutsu, which would be a huge addition to his combat abilities. And, his own Sage Mode could be enhanced by Madara's power, allowing him to be even more powerful in battle.
In this fanfiction scenario, Naruto could gain some extraordinary powers. For one, he might inherit Madara's ability to regenerate quickly, which would make him even more difficult to defeat in combat. He could also gain an understanding of the Uchiha's unique chakra nature and be able to blend it with his own Uzumaki chakra. This could result in new and powerful jutsu that no one has ever seen before. Additionally, Naruto may be able to tap into Madara's battle experience and instincts, making him a more formidable fighter in both one - on - one battles and large - scale warfare.
He might gain some of Madara's Sharingan - related abilities. Maybe he could use some of the advanced genjutsu techniques that Madara was proficient in. Since Madara had strong chakra, Naruto could also potentially have an increase in his own chakra levels or a new way to manipulate chakra, like Madara's ability to control the Susanoo.
He might gain Minato's teleportation jutsu. It was one of Minato's signature moves, and with Minato sealed in him, Naruto could potentially access and learn this powerful technique.
He might gain the ability to use his parents' chakra more directly. For example, if his father was good at a certain type of jutsu, Naruto could potentially access that more easily. Maybe some kind of enhanced speed or strength that was unique to his father.
If Naruto became an Ino fan due to Kyuubi's influence, he might gain some mental fortitude. Ino is good at mind - related jutsu, and Naruto could learn from her how to better protect his mind from enemy attacks. Maybe he'd start to develop a form of mental shielding similar to Ino's techniques.
He could potentially gain an enhanced understanding of wood - style techniques. Since Hashirama was a master of it, Naruto might learn how to create more complex and powerful wood constructs, like huge forests for both offense and defense.
Naruto would likely gain the ability to use all six paths techniques. The Rinnegan allows the user to manipulate gravity, as seen when Madara used it. Naruto could use this to enhance his combat skills, for example, pulling enemies towards him or pushing them away forcefully. He could also use the Preta Path to absorb chakra, which would be a great addition to his already large chakra reserves.
Naruto would gain some really cool (pun intended) new abilities. The ice - making ability would be the most prominent. He could form ice clones, similar to his shadow clones but with the added advantage of being made of ice and potentially having more durability. His sensory abilities might also be enhanced, as Esdeath has a good sense of her surroundings when using her powers. He could detect enemies hidden in the ice or snow. And, like I said before, the time - freezing power. This would allow him to analyze his opponents' moves during the frozen time and come up with the perfect counter - attack. It would add a whole new dimension to his combat skills.
In some Naruto fanfictions, Madara might be sealed through a powerful jutsu created by the main character. For example, the protagonist could combine different elemental chakra natures to form a unique sealing technique specifically designed to counter Madara's power.
He might gain a deeper understanding and control over the Six Paths powers. Maybe he can access different levels of chakra that were previously unknown. For example, he could have a more direct connection to the natural energy around him, allowing for more powerful and precise jutsu.
He could potentially gain some form of Sharingan - like ability. Since the Sharingan is a signature Uchiha power, it makes sense that if Naruto were acting like an Uchiha, he'd develop something similar. Maybe a version of it that combines with his own Uzumaki chakra, creating a unique and powerful new ability. He might also gain better control over fire - based jutsu, as the Uchihas are often associated with fire. And perhaps enhanced perception skills, which are also characteristics of the Sharingan.
Naruto could gain enhanced senses from the Ghost Rider powers. In the Naruto world, this would help him in detecting hidden enemies or traps more easily. The ability to ride the flaming motorcycle would also be a new skill. This could be used for quick transportation during missions or battles. He could also gain the power of transformation into the Ghost Rider form, which not only gives him a more intimidating look but also access to all the other Ghost Rider abilities. And with the Ghost Rider's connection to the spirit world, Naruto might be able to communicate with spirits in the Naruto universe, which could lead to new plot developments.