Last time I checked, having the same powers as the sage didn't make him his successor. Everyone who obtained the rinnegan or the Juubi claimed to be the new So6p, but only those who inherited Ninshu and has been acknowledged by the sage, would be his successor. That person is Naruto.
He only gave Sasuke power to prevent the repeat of Indra and Ashura, but he even said afterwards that he knew Sasuke would turn on Naruto. It was Naruto who ended the feud and made Sasuke his support, just like how the sage wanted Indra to support Ashura. In reality, Naruto is the new sage, because he inherited Ninshu and has been acknowledged by the sage.
So, it's just people's own fanfic to call him the new so6p, when he wasn't even acknowledge by the sage as his successor. Like the sage said, he didn't spread chakra to make it a weapon, but to connect people in order for them to understand each other. That's why having abilities on par with the sage, doesn't make Sasuke his successor.
Also, Sasuke isn't even a sage.
Indra didn't even inherit the rinnegan from the sage. How do you expect Sasuke's power to be inherited by Sarada?
I can see her reaching MS, with all the abilities of EMS, because of a stronger eye power, you know, since it was claimed that the Uchiha's eye power degraded over the generations, so I assume that at one point their eye power didn't weaken in MS form, like Sasuke's, but there's no way she can achieve EMS on her own without taking the eyes of a relative.