Of course, as with many speculations, this theory assumes a lot of the “hints” in Star Wars: The Force Awakens are deliberately connected rather than just coincidental.
By the end of the video, the narrator explains how when push comes to shove, having Rey as Palpatine’s granddaughter would be interesting storytelling.
You can watch the video below to see the Rey/Palpatine theory unfold in its entirety.
He seemed like the kind of guy who was married to his work, i.e. plotting and inflicting pain with his Sith abilities.