Nice reply
Alright here I will expound upon my assertions. Naruto lacks variety in his arsenal. Having the Rinnegan mitigates that.
But first I will talk about BM Sage Mode, which will presumably come first.
BM Sage Mode:
Taught and learned by the toads, the advantages afforded to those who study senjutsu from the toads include:
The user's physical strength, speed, stamina, reflexes, perception and durability dramatically increase.
The user's ninjutsu, genjutsu, and taijutsu become more powerful.
The user can harness the natural energy surrounding them, turning it into an extension of their body, which increases the reach of their attacks.
The user gains the ability to sense chakra around them.
As stated above (From the Wikia) basically Naruto becomes a lot more powerful. He becomes an amazing sensor, his ninjutsu techniques are increased, he's faster and he's a Taijutsu monster. Everything around him is an extension of himself because of the nature chakra. But the biggest asset here is; The amplification of his techniques. For us to know this, we need to analyze BM as well.
BM Mode:
"While in this form, Naruto's speed and strength are enhanced greatly to such an extent that he was able to deflect five Tailed Beast Balls by simply moving past them.[59] With the help of a shadow clone, he could even move fast enough to two different locations of a battlefield, while at the same time, destroying Madara Uchiha's wooden dragon in the process.[60][61] He is also capable of using the Rasengan and the Super Mini-Tailed Beast Ball without the aid of his shadow clones,[62][63] as well as create two Rasenshuriken in both of his hands at the same time.[64]"
As stated here, he becomes faster, stronger AND he can use Rasengan AND Rasenshuriken with one hand (Even doing a double RasenShurkien). What does this mean? Sage Mode's multipliers will apply to the massive boost BM gives.
So hypothetically, a half Kurama is able to equal 6 other TBB's. A full Kurama in theory should be able to overpower them. NOW, add in the Sage Mode amplifier... That is practically on Juubi scale.
So in hindsight this mode gives him:
- Immense reflexes (Due to Sage Mode)
- Master Sensory (Sage Mode+ Bijuu Mode)
- A TBB on the Juubi's scale (Not quite, but the multipliers signify something in the vicinity of such)
- Frog Kata which aids in making him a Taijutsu monster
- Ability to use RasenShuriken with one hand, and use two at once.
Boss! But the problem is... SM Hashirama stomps because of Mokuton suppression (Established in the OP)
In comes Rikudou Mode Naruto!
Add the Rinnegan on to the aforementioned form.
What this allows Naruto to do: Let's him use all 5 Elements and access to the hidden Sixth Element, Yin-Yang Release (Which will be needed to split the Juubi), lets him get people in close to attack them (Deva Path), lets him guard his blind spot with multiple arms (Asura), guard against large scale techniques (Preta) etc...
Basically it allows Naruto to be A HELL of a lot more versatile than before.
Because of Naruto's inherent reserves+BM, he could theoretically make a Chibaku Tensei on the scale of the Moon like the Sage, his Shinra's Tensei's would be larger than Nagato's (Because of more chakra output) and his Chou Shinra tensei could decimate more than just the Leaf Village. Not to mention Naruto can now utilize different chakra natures which would help in different situations AND he can make a Rasengan variant for each chakra nature.
