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.