I don't think the cult will happen
And I hope not. It's been too theorized, everyone would see it coming. Kevin Williamson got to do this already and it was called The Following, a fun enough show.
Heck give us something more surprising. Ghost Face is Maureen, she's been secretly alive the whole time and orchestrating everything, to get revenge on Sidney for having a secret affair with Cotton herself, that'd be more messed up