Sasuke went through the same process as Madara,he had senju dna and near death experience.It will be odd for him to unlock one instead of 2,if he only have one sharinnega then the other eye is the rinnegan because of the senju dna
Considering that He have half Hagoromo chakra (Yin like Indra chakra), He unlocked one Rinnegan.
Madara achieved pair of rinnegan by have both chakra ( Ashura and Indra chakra mixed into Hagoromo)
If Sasuke have Naruto chakra ( Yang like Ashura chakra) he will have two rinnegan, i believe.