I believe that Sasuke might unlock the rinnegan at this point.
Madara said he unlocked it when was near death basically.
Sasuke is about to die, so maybe you could only unlock the rinnegan in critical moments just like the sharingan.
Madara also said u could only activate the rinnegan by having both senju and uchiha power
Sasuke is already an uchiha so that part is taken care of. Hashirama gave sasuke his chakra so now he
has senju chakra as well now.
So im guessing he might unlock the rinnegan at this point because it looks like it's setup that way.
Let me know if you agree or not, give good reasons as well, no fanboy/fangirl answers