There are videos on Youtube with people analyzing this and finding hints in the animated Star Wars show and elsewhere, I think. The main part of said theory is about the dark/light, black/white or sith/jedi conflict or aspect of the series. I'm also mixing my own thoughts into this.
I didn't really care too much about the specifics of the hints and what it all might mean exactly, but I find this interesting from a structural perspective. When you think about George Lucas saying Star Wars mirrors itself.. so far we have two completed trilogies, mirroring each other. I'll only pick the first movie of each one for now:
The Phantom Menace -> Anakin - Sith - Dark/Black
A New Hope -> Luke - Jedi - Light/White
So what about the third one?
The Force Awakens - Rey? - Neither sith nor jedi? - Balanced? Grey?
Menace is negative, hope positive.. awakening could be both, it's neutral. It could also be what happened during that final lightsaber duel - the Force awoke in Rey, that's how she was able to fight Kylo Ren off like that. And it might be a balanced version of it, the whole of the Force. Stronger than any "half"-version of it. Maybe even the extended fulfilment of the prophecy of the chosen one bringing balance. I think that's where the Skywalker story could be headed in the end. A new way of utilizing the force, embracing both of its sides, being grey instead of black or white.
Sure, there weren't any signs of Rey making use of any sith powers or something. But that whole black/white/grey, sith/jedi/balance, Anakin/Luke/Rey structure seems to make a lot of sense to me. Doing grey after black and white have been done just seems logical if you wanna maintain some form of mirroring.