More thoughts. If Rey's parents were prominent in the original Empire, it would explain why few knew of her existence. She would have been in danger from rivals in the Imperial remnants, until one or both of her parents managed to get her away before losing themselves as well.
There is already a similar saga in Rogue One. The daughter of an Imperial Officer is left to fend for herself in the wilderness, later rising to fulfill her Father's wishes. So it's possible that Rey would later turn against Luke once she realizes this. Especially if Snoke, who knows so much about the last days of the Empire (possibly from her father), sets the record straight before her.
The civil war among Luke's acolytes could be due to some like Kylo Ren wanting him to become the Jedi overlord of the new republic. This would have prompted Luke to exile himself, and would explain why the New Republic was not officially keen in getting him back.