Trying to wrap my head around this..

[voids]

Rikudo chakra is only needed to awaken the rinnegan not to maintain it, it's like saying you need Uchiha chakra to maintain a Sharingan

You do need Uchiha chakra, but that comes from the sharingan eye and seeps into the hosts chakra. That's how I believe Kakash was able to use it without being an Uchiha. All living organs produce chakra, the eye would produce a small amount of uchiha chakra at all times and that chakra would be the same as the original hosts chakra.

 

[voids]

Changes in an Uchiha's brain are visible as changes in their eyes (sharingan, etc.)

Once the brain changes, the eye will retain its appearance - specifically, the associated powers won't go away.

There were no brain changes. His brain did not change to get this. All he needed was to be given half of the sages chakra. This has nothing do with how the 3T changes to MS which changes into EMS. The process of Sasuke's sharinnegan is completely different as only chakra for the sage was required.

 

[Kirokill]

I'm not sure if he lost his rage sage mode or not. Since there is no big threat I doubt he'll ever rage.

 

[voids]

I'm not sure if he lost his rage sage mode or not. Since there is no big threat I doubt he'll ever rage.

It's Rikudo Sage Mode. Not rage...

 

[1Told]

that's just some obvious bad mouthing OP, let them talk Lol

it's pretty logic that he didn't lost it just because he didn't use it in the movie, SP started working on the movie in 2012 btw so RSM didn't exist at that time in the manga but only in Kishimoto's head or in pre-drawings he already made.

he probably never explained it to them, not the first time it happened (SP talked about other things Kishimoto told them very late during the process of making the movie in their official website) and that would explain why Sasuke didn't use his full power too and why his scene is just 15sec long, seems like something they put in the movie at the last minute...