It would be a shame if Star Wars: Episode IX wasn’t left with anything fascinating to explore.
As Maz Kanata says, that lightsaber first belonged to Luke, and Anakin before him.
That seems like proof Rey is part of the legacy, though plot details from the canon novel Bloodline and the revelation she never met Kylo Ren prior to Force Awakens throw monkey wrenches in the theory.
It sounds like fans will be fervently pouring over anything they can get their hands on in an attempt to figure it all out until Star Wars 9 premieres in 2019.