.....To the OP. Yeah. Sounds plausible. The SAGE obviously received a watered down version of the Eye of God.... The Samsara Eye. Kaguya had the third Eye, so it could have been inherited from that power.
His brother could have survived and gone into obscurity, but propagated the Hyuuga clan. The story over The Byakugan and Sharingan being derived from one or the other isn't entirely true in the end. They are a shared lineage split apart at the birth of the two brothers. Just my opinion of course.