There's actually a LOT more than suggestion that she is indeed Luke's daughter. I've actually had this rant in person with rd95, and laid out my entire case. First off, Her name is 1 letter away from the book 7,8,9 name for Luke's daughter, Jeyna (or REYna amirite?). Second, the saber that was her grandfathers (even if it was THE YOUNGLING-STABBER, talk about a family legacy), then her fathers, and is now "calling out to her", and is waiting for family who dropped her off to put her into hiding so that she wouldn't be chased by the renegade jedi from the academy. Now lastly, lets go to the trailer: "THE FORCE IS STRONG IN MY FAMILY. MY FATHER HAD IT. I HAVE IT. AND YOU HAVE IT." So not to even talk about the TFA video game slip where Kylo calls Rey "COUSIN" and Disney is immediately shutting down any and all talk about it when it was posted, we have to look at the fact that honestly it sounds like making Rey's heritage a reveal was like a last minute thought to be a secret. Or else that trailer wouldn't have even been a thing. Disney is being a little hamhanded here. Not even subtle at all.