I'm not quite sure what I think of that idea. If Luke is the father, then he probably never knew he had a daughter (Rey). How else can her presence on that desert planet be explained? Because if Luke were aware of her existence, I would (hopefully) think he, who never knew his own parents, would not leave her all alone out there, waiting. (And Leia and Han certainly didn't know her.) For Luke's sake, I keep thinking that I don't want him to be her father. Think of all the anguish she might throw at him.