Rey IS a Skywalker, but she would not be Luke's daughter. Probably realizing from chats from Obi wan and Yoda spirits perhaps Luke understands the origin of his own existence (Anakin's weakness for Padme) and when Han and Leia had a family (Leia is not a full jedi knight) the children of Anakin had to make that fateful decision that became the basis of their lives: separation and hidden "until the time was right."
Success in Maz's "cave": when Rey touches the light sabre she goes in with her fear she not only experiences her own past but also Luke's failure on Bespin (note the tunnel from Cloud City image and audio track of Luke's horrific realization of Vader's revelation) turn into her own abandonment and then the focus on the second jedi purge leading to her future confrontation with Kylo in the snowy forest, not the green forest. I'm sure they could have shown us a little of Mostafar to really show the full impact of Anakin's lightsabre.
Besides the all of the force/jedi implications, Rey's abilities to tinker around matches grandpa (Anakin) and Han's especially with the Falcon.
Snoke (if he is Plaegis the wise) knows that Rey could at last be his true successor and that he has a chance to defeat the jedi. The whole symbolism around ren and rey is like siblings not cousins.
May the force be with us.