Theory: The first star wars saga centered around a Father/son relationship. This next one will center around Daughter/Mother relationship.
Reason: If Rey is Lukes daughter, and I believe she is, then the question remains where is her mother and who is she? Luke is alone. So, she's either dead or as I suspect she is working as a sith Lord for Snoke. This also answers the question, in part on how Ben was lured to the dark side.
The books call her Mara Jade, who tried to kill Luke on several occasions, but Luke was able to bring her to the light.
So I believe Luke and his wife started a training academy with Ben Solo as one of the top pupils. Luke's wife probably secretly spoon fed Ben things about the dark side not knowing he would become infatuated and obsessed with his grandfather Vadar. Ben Solo eventually becomes semi seduced, goes rogue, and probably kills someone or someone(s) in the academy and runs away.
Lukes wife still feeling that pull leaves Luke as well...it is She who will completes Kylo Rens training and it is she who will eventually kill Luke.
So Luke will train his daughter, while Lukes wife, "Mara Jade?" will complete Kylos training, her nephew...
So two perhaps three epic confrontations will occur.
1) Luke vs. His Wife
2) Rey vs. Ren
3) Rey vs. Her Mother
It also could be that Kylo killed Lukes wife and that turns this theory in a new direction.