WARNING RAMBLING BELOW.
Technically a child from Naruto should be an Uzumaki (although technically Naruto should have been a Namikaze) but what I meant is that the child would have the Sharingan and pass it on in effect restarting the the Uchiha, maybe even being named Uchiha in honor of the gift Sasuke would have given Naruto. It is mentioned that the Sharingan, Byakugan and Rinnegan all came from the Sage but nothing has been said to my knowledge about what would happen if a Hyuuga and an Uchiha had a child or if either was mixed with a Rinnegan user.
I'm thinking something similar to what happened to Gaara will happen with Naruto perhaps with the 5th using her stored chakra power to revive him at the cost of her own life or that Sakura will use the jutsu she saw used to revive Gaara and sacrifice herself (it would be a fitting end to a character who mostly just got in the way.) I think if it does happen it will be because Sasuke captured him, which will lead to the guilt that eventually causes him to sacrifice himself to make amends. Of course there is also the possibility that the half of the Kyuubi not sealed in Naruto could be retrieved and used without the half in Naruto still allowing the Juubi to be remade. I think I like the idea of Sakura and Sasuke both giving their lives to Naruto so he can save the world the most.
As far as Naruto being Senju, I'm pretty sure that is where all the hints are leading. We still don't know much about Kushina or Minato but I'm willing to bet one of them was Senju. Perhaps even a direct descendent of the Sage of the Six Paths, the lore covers the brothers who inherited the body and the eyes but seems to leave out a lot between their time and that of Madara and Hashirama. That pretty much means anyone could be Senju. Especially considering in the early days there were no hidden villages and the Senju and Uchiha travelled the world hiring out to whoever and whenever. It would also fit the opposites of appearance between Naruto and Sasuke and Madara and Minato if we eventually find out the Sages younger son was blond and that Minato is a direct descendant. That said, I still think that Naruto will get his Senju blood from Kushina unless there is something not yet revealed planned for her contribution to Naruto (like a new blood line limit or a special affinity.)
The reason I think that things will play out this way (or close to it) is because of the story about the Juubi and the Sage of the Six Paths. It took the Sage who had both the eyes of the Rinnegan and the body of the Senju combined to absorb the Juubi and eventually separate it into the 9 tailed beasts. If Madara manages to put it back together it will take a second coming of the Sage to do it all again and save the world from chaos. I think that is the likely direction the story is headed and I think that in the end Naruto will have to take on that challenge.
The whole Moon's Eye plan just seems like a great way to retrieve the body of the Juubi which the Sage was said to have sealed in the moon and could backfire on Madara by bringing the Juubi back into being while Madara doesn't have everything necessary (namely the Senju body) to seal it inside himself and control it. If he seals it in himself I think it will take control of him and either use him to get it's body back or just use his. If he manages to seal it and then project his MS on the moon I think that will draw the Juubi's body back to the world and reform the Juubi that way. In either case I think Madara will cause the Juubi to be unleashed on the world again and Naruto will have to stop it.
Just some things I had on my mind.
NOTE - LONG EXPLANATION
I believe Naruto has a secret kekkei genkai ability that is unknown to most everyone in the series. The following theory will attempt to prove this possiblity.
The first piece of evidence that supports my theory is a statement by Yamato. In chapter 299, entitled "The Source of Strength", Yamato makes the following observations about the Kyuubi's chakra:
Naruto Chapter 299 page 4
"The Kyuubi's chakra is acting like poison...entering through her wound. Something like that can't simply be healed by Sakura's level of healing jutsu. Which makes me even more surprised that Naruto is able to endure it."
Just a few pages later Yamato makes the following statement while speaking to Naruto:
Naruto chapter 299 page 11
"Your true strength isn't from Kyuubi's power, and the reason you're able to stand Kyuubi's chakra is because of the strength of your own chakra."
The above quote implies that Naruto's own chakra holds some special properties that normal people's chakra lack. Naruto, on his own can withstand the negative effects of the Kyuubi's chakra. This is a fact supported by the manga itself.
There are currently only two known kekkei genkai abilities that can control the Kyuubi's chakra. The first is the Mangekyou Sharingan as noted here & here. While unconfirmed, it is believed that Mangekyou Sharingan controls the Kyuubi through the use of genjutsu. It is quite obvious that Naruto has neither Mangekyou Sharingan or genjutsu strong enough to control the Kyuubi. The only other known kekkei genkai that possesses the ability to control Kyuubi chakra is the unnamed kekkei genkai ability of Hashirama Senju, the first hokage. Yamato, a clone of Hashirama demonstrates this ability here & here. He then explains why only he can use the ability here & here
It is my belief that the hidden kekkei genkai that Naruto possesses is the same one Hashirama Senju had. I also believe that Haku of the land of water also had this ability. The abilities of Haku & Hashirama were simply named after the elements they created by combining their elemental affinities. Hashirama's being Mokuton(earth+water) & Haku's being Hyouton(wind+water). I believe their abilities came from the same source. That source is the kekkei genkai(bloodline limit) of the Uzumaki clan.
The Uzumaki clan is a complete unknown at this point, however we do known Naruto's mother was from the Uzumaki clan, as well as the Whirlpool Country. It is possible that the former Whirlpool Country was the home of the Uzumaki clan, however something happened to the Whirlpool Country. Since it is refered to as the "former" Whirlpool Country, it is safe to assume something happened to the country to cause it to no longer exist. I believe there are only two possible answers for what happened to the Whirlpool Country, it was either completely destroyed by some event/natural disaster or it was overthrown & renamed by the invaders. I believe it was the later. The Whirlpool Country was overthrown by a coup de'tat, led by none other than Madara Uchiha(I'll elaborate on this further later).
Kushina Uzumaki was from the ruling family of the Uzumaki clan, she was saved from certain death during the coup de'tat & taken to Konoha to be with her distant cousins the Senjus. Hashirama & his brother were the sons of an Uzumaki mother. It is the Uzumaki women that carry the kekkei genkai of the Uzumaki clan. Hashirama's mother married a man from the Senju of the Forest. It is my belief that Hashirama got his earth elemental affinity from his father & his water elemental affinity from his mother. This would also explain why Nidaime was so skilled with his water elemental jutsu. The affinity for water is most likely pasted down through the Uzumaki genes in a similiar manner to the fire elemental affinity of the Uchiha clan. Kushina would have known of the Uzumaki's clan kekkei genkai & she would have been able to tell Minato that their child would have had the possiblity of containing the Kyuubi.
There are two things that further reinforce my belief. Kishimoto often uses symbolism to hint at certain plot points. I believe the following instances of symbolism point to a connection betweeb Naruto & Hashirama Senju:
Naruto chapter 1 page 1
Naruto has just defaced the Hokage monument, he even signs his work. The funny thing about this is where Naruto signs his name. Naruto's name appears on Hashirama, the Shodaime Hokage & Minato Namikaze, the Yondaime Hokage. One of these men has already been revealed to be Naruto's father, could the other also have a blood relation to Naruto?
Also, to prove that what Naruto places on the Hokage monument is indeed the signature of his last name Uzumaki, I offer this, Naruto's signature on the summoning pact he made with Gamabunta. Naruto signs the name Uzumaki with the same spiral he wears as a clan symbol. The spiral is the symbol of the Uzumaki clan.
To further show the connection between Hashirama & Naruto, we simply need to look at the uniform of all Konoha ninja. The uniform has the spiral symbol of the Uzumaki. It is my belief that Hashirama did this to pay tribute to the source of his kekkei genaki, the same kekkei genkai that allowed him to defeat Madara Uchiha. During his battle with Madara Uchiha, Hashirama wore the uniform of the Senju clan, however after that event the Senju clan's uniform was no longer used.
Then there is that defining moment at the Valley of the End, were Naruto stood on Hashirama's head & Sasuke on Madara's head, here. There is also the fact that Naruto is in possession of Hashirama's chakra crystal necklace. The very necklace that Hashirama used to control bijuu, why give Naruto this necklace if he will never make use of it?
Now, I also believe that Haku share the same blood as Naruto & Hashirama. I believe that the current Water Country was once the former Whirlpool Country. Madara Uchiha after his defeat at the hands of Hashirama, took the opportunity his apparent death gave him to leave the land of fire. Madara Uchiha went in search of the source of Hashirama's power & he found it. Madara Uchiha learned that Hashirama was a descended of the Uzumaki clan & that the Uzumaki clan had a special kekkei genkai. Madara wanted to destory the source of Hashirama Senju's power, so he started a rebellion against the Uzumaki clan, rulers of the then Whirlpool Country. The civil war lead to the death of many Uzumaki clan members as well as other clans with kekkei genkai abilities from the Whirlpool Country. Madara's side won & the Whirlpool Country was renamed the Water Country. Madara became the Mizukage. Those with kekkei genkai abilities were persecuted, those who were still alive went into hiding.
Haku's mother was one of the Uzumaki clan members that survived, she fled to the snowy northern region of the now Water Country. Their she met a man & got married. She eventually gave birth to Haku, of course you know what happened next. Haku discovered the Uzumaki clan's kekkei genkai on his own. His father then killed his mother & Haku killed his father & the other villagers in self defense. Those with kekkei genkai abilities were considered the cause of the civil war, so they were always hunted & killed. Haku met Zabuza & they begin their journey together. Haku combined his water elemental chakra & wind elemental chakra to create Hyouton(the ice element). Haku used his elemental affinities to create Hyouton because he was born in a snowy region of the Water Country & it was natural for him to create ice.
In conclusion, it is my belief that Naruto possesses the same kekkei genkai as Hashirama Senju & Haku of the Water Country. Naruto's second elemental affinity will be water & he will use his kekkei genkai to combine his wind & water elemental affinities to create a rain/storm element. Since Naruto is from a warmer climate this will be more natural for him, but he might also be able to create Hyouton. Naruto will be able to control the rain itself. He will also be able to create whirlpools & tidalwaves as well. Naruto may also discover a third elemental affinity for earth, allowing him to use Mokuton as well. Another thing is since Naruto possesses Shodaime's chakra crystal necklace, he will receive the same benefit that Shodaime did. Naruto will be able to bend Bijuu's & their chakra to his will. The only thing keeping Naruto's kekkei genkai from manifesting is the Kyuubi. Naruto will eventually lose the Kyuubi, but I'll save that for another theory.