Most of us have heard, just about every possible what if, in regards to Rey's lineage. A lot of them are plausible, and I do not wish to take anything away from those theories. There is an obvious, bigger story to her and how she seems to have the ability to tap into the Force, nearly effortlessly. How with a glaring mismatch of training, she was not only able to keep Kylo Ren at bay, but get the upper hand on him.
I had a theory before VII came out, that Luke was a Gray Jedi. Is it possible that he is Rey's father, but not in a manner that would be considered conventional? I submit that as a Gray, Luke may have inadvertently or on purpose, manipulated the midi-chlorians, to produce a child, Rey. Her mother, then left her on Jakku, for reasons that are unclear. Perhaps her mother is Captain Phasma, how would that be for a twist? But I digress, as a Gray, Luke would have become educated in both the light and dark sides of the Force, without surrendering to either, balance? Luke, being hunted relentlessly by the First Order, to extinguish the last of the Jedi, might have made a decision to ensure a future generation of Jedi. Luke could have then imprinted his lightsaber to recognize her, and call to her, imprint upon her a Jedi introduction crash course; much like the effect on R2-D2, to know the precise moment to awaken. Sending Rey to him, in order to complete her training.
Luke's time in exile, was not spent, crying in his Corellian nectar, I am assuming. Given that we know, Yoda, Kenobi, Qui-Gon and Anakin, had the ability to Force Ghost, are there others? Yoda is the voice, Rey hears, when she touched Luke's lightsaber, maybe it was him Force ghosting. Is it possible that he has learned to transfer some knowledge directly into the mind of others? Maybe VIII should start out with Luke, reaching for the lightsaber, as he touches it, Rey's origin flashes, but only bits and pieces, who wants to know too much, too soon, right?
Or maybe Rey and Ben, were switched at birth, I guess we will find out in a couple of years.... Until then, May The force Be With You...