Indra right now , is possesing Madara , but let's look in the past .
When Madara left the village , he was obviously possesed by Indra . When Madara found Obito , he was still possesed by Indra . When Obito changed his ideals and decided to join Madara , the moment Madara cut his ties with Gedo Mazo , Indra started to posses Obito . And this pretty much explains why Edo Tensei Madara was not possesed by Indra . So , the moment Obito changed his ideals again , Madara got revived in his prime , and , that's when Madara got possesed by Indra again .
About Sasuke , he was never possesed by Indra . Indra was said to be a genius . Sasuke was never like that . Madara was , and Obito continued his legacy . Now that Obito betrayed him , Indra left Obito to posses Madara again .
Thanks for reading . u_u
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Orochimaru , a child prodigy, a genius among geniuses, who got praised by almost everyone and he also had solution for pretty much everything(he even cancelled RDS) hypes , Sasuke as a genius who makes himself pitiful if compared to him.
This is the hype of highest rank(in terms of intelligence) given to anyone in the manga. (because a extremely genius ninja admits that a ninja is leagues above him in terms of intelligence)
Edit :
Secondly,
Indra and ashura were rivals.
IF ashura was possessed by naruto, someone of the same generation must be possessed by indra.
If we talk about rivals of naruto, the first guy comes that comes to mind is Sasuke.
And this time naruto is the one who will lose against sasuke.
Naruto thinks ninja must endure, so he must lose and he must endure it and admit inferiority to sasuke.
Only then a god like ninja (his pet calls him lord, he was stated to have god like speed in databook) like sasuke would be satisfied and only then curse of hatred must be over.
Something different must happen and that history must not repeat itself, only then the curse of hatred will break.
TL;DR , sasuke is indra, he will beat naruto in the end, curse of hatred will end, indra's spirit will be satisfied, ashura's spirit would just deal with it, sasuke becomes hokage, he changes the system and balance everything , everyone is happy.
also chakra is given back to juubi and juubi is sent to some other planet because concept of chakra certainly didnt help the ninja world.