Shouldn't that have happened already when Kakashi Raikiri stabbed Obito and Minato later sliced through him? I don't think it'll happen, you need the same pair of eyes in order to awaken the Sharingan's full potential. At least that's what Madara said.
Senju and uchiha is needed because the rinengan is a progentor gene although since there is a whole generation between the sage and the uchiah and senju the chances are still slim that it will be awakened
Besides he will never take the rinnegan over kamui
No Madara got it when his original life span was almost over. It took him years to activate it. Just because Obito has senju DNA doesnt mean hes going to get it, and if he does he'll most likely only get it if he lives for a long long time.
It has actually never been said you NEED ems to unlock rinnegan. Or even sharingan.
The only thing that we know for certain, is that you need senju dna and uchiha dna to unlock rinnegan.
Then you must go through the unknown trigger mechanism to unlock. It is assumed that the trigger mechanism is when you are dieing. It is more likely it is caused by the extreme emotions that would come from dieing.
Madara actually said that obito would have a chance to unlock his own rinnegan. See top left corner
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"Even if you dont awaken the rinnegan you can still control the mazou"
That was VERY clear. That was just after he said "You cant awaken the rinnegan without the senjus and uchihas powers"
Madara clearly believe it was POSSIBLE for him to awaken the rinnegan. Or he would not have said that.
That would also mean it is possible to awaken the rinnegan with just 1 eye.
As madara had also said before, that "you need to have both eyes to awaken their full potential"
It is possible without both rinnegans, you cant perform the rinnegan techniques properly. This is just speculation, but it could explain why we never saw a shinra tensei or any of the paths. We know obito can perform the outer paths( useing the edo jins, etc)
In all the talk of the rinnegan, it hasnt been said that you need a ems to unlock it. The only thing ems does, is reduce strain of a ms users eye, and give them a permanent light(as well as perhaps a new technique).
It makes less sense to me that someone would have to kill their relative with ms, just to get ems to then get rinnegan.
Last i checked the equation for rinnegan was Uchiha+Senju+Awakening event=rinnegan.
Not Uchiha+Uchiha+Senju+Awakening event=rinnegan.
I dont think you even need to have awakened the sharingan to awaken the rinnegan.
Obito skipped awakening his 3rd tomoe, because he experianced the trauma needed to awaken the MS(tragic death of a loved one)
To awaken sharingan, you need to experiance severe stress/trauma (ie obito in need to protect kakashi and about to be killed, and sasuke when he was nearly getting killed by haku(and previously when itachi killed his parents))
So to unlock rinnegan, you have to experiance a even greater emotion(im not sure if it would be a negative one though...its possible to unlock rinnegan, you have to just give up on the world or something(just speculation though)
So i hope i have shown that I have given evidence, that supports the fact that senju+uchiha+a specific emotional state=Rinnegan
Not EMS+Senju dna+specific emotional state= rinnegan
AGAIN. IT HAS NEVER BEEN STATED ANYWHERE THAT YOU NEED EMS TO GET RINNEGAN. PERIOD. IT HAS NOT EVEN BEEN STATED YOU NEED MS OR EVEN SHARINGAN ITSELF. JUST senju dna and uchiha dna.And whatever emotions needed to unlock it from there.(now you may need to have more pure senju dna and more pure uchiha dna to do so. But this part is unknown)
I have long thought(since at least the obito survival backstory) that obito will probably unlock rinnegan in his eye(and kakashis) in the very end(ie he is dieing or something)
It is possible for him to awaken his own rinnegan. How likely I dont really know.
As obito has his own uchiha dna, and a proven rinnegan unlocking senju dna(hashi on madara), he has all he needs to unlock a rinnegan(minus the emotional state needed)