I doubt that leak is legitimate. Disney are evidently trying to distance themselves from the prequel trilogy with the winding down of the Clone Wars series and next to no prequel references in The Force Awakens or the Rouge One trailer. So having a central plot twist that is dependent on the prequel trilogy would go against that trend.
The Snoke = Darth Plagueis theory seems likely though. The music that plays in their respective scenes is the same and it would tie the stories together without requiring that the viewer watch the prequels (since Plagueis is only mentioned briefly in episode 3), rather than introducing a brand new enemy adhoc.
The Han Solo thing was leaked early, so I’d be weary about what we hear. It might come close to what we get. With that many people working on a movie, something is bound to surface when it’s not supposed to…
And also, isn’t the “Luke is Rey’s father” thing just a little too obvious? That’s why what was said in the leak makes a little more sense. Throwing something unexpected at the viewer rather than what they’re expecting…
In the second Force Awakens trailer, Luke says “The force is strong in my family. My father has, I have it, my sister has it, you have that power too.” It seems very likely that the words are directed at Rey, the latest member of the Skywalker family. I think the important question isn’t if Rey is Luke’s daughter, but why she was left behind on Jakku.