The important thing is not how Naruto and Sasuke will get their arms back its why they lost them.
-As you can see in the page where they both have their arms cut off there is a panel where their blood is mixing together
-Although this could be a symbolic moment where it shows how they're connected I believe otherwise
Logically, there are two possibilities that really stand out why the blood is touching that will cause the story line to move along
1. The mixing of the blood will cause Hago to come out again
-When Hago last appeared it was cause Hashi touched Madara's lower body
-Hago stated that this was due to the mix of Ashura, Indra, and Kyubi's chakra
-Right now, Naruto has half the Kyubi in him as well as Ashura's chakra and Sasuke has Indra's
-Therefore, the mixing of the blood could cause Hago to reappear
This would be significant to the story because Hago would be able to congratulate them on ending the cycle blah blah blah and we will finally get a close on at least his half of the story
(Im sure more will be revealed about Hamura and Kaguya in the Last movie or at least I hope so)
2. The mixing of the blood will end IT
-As Hago stated, the way to release IT was to mix the power of the tailed beasts that Naruto has and the rinnegan that Sasuke has
-The mixing of their blood and chakra therefore could be the catalyst for IT to being released
This would be significant to the story for obvious reasons such as it saves time for the conclusion to be finished as it would be a waste of time to see Naruto and Sasuke to get back to full health before releasing IT
To summarize, Naruto and Sasuke didn't just lose their arms for the sake of losing their arms, but instead it will help progress the storyline in the fastest way possible
-As you can see in the page where they both have their arms cut off there is a panel where their blood is mixing together
-Although this could be a symbolic moment where it shows how they're connected I believe otherwise
Logically, there are two possibilities that really stand out why the blood is touching that will cause the story line to move along
1. The mixing of the blood will cause Hago to come out again
-When Hago last appeared it was cause Hashi touched Madara's lower body
-Hago stated that this was due to the mix of Ashura, Indra, and Kyubi's chakra
-Right now, Naruto has half the Kyubi in him as well as Ashura's chakra and Sasuke has Indra's
-Therefore, the mixing of the blood could cause Hago to reappear
This would be significant to the story because Hago would be able to congratulate them on ending the cycle blah blah blah and we will finally get a close on at least his half of the story
(Im sure more will be revealed about Hamura and Kaguya in the Last movie or at least I hope so)
2. The mixing of the blood will end IT
-As Hago stated, the way to release IT was to mix the power of the tailed beasts that Naruto has and the rinnegan that Sasuke has
-The mixing of their blood and chakra therefore could be the catalyst for IT to being released
This would be significant to the story for obvious reasons such as it saves time for the conclusion to be finished as it would be a waste of time to see Naruto and Sasuke to get back to full health before releasing IT
To summarize, Naruto and Sasuke didn't just lose their arms for the sake of losing their arms, but instead it will help progress the storyline in the fastest way possible