Rumored script spoilers that I kind of believe:
1. Sidney gets attacked in the opening, but lives.
2. Dewey dies
3. The killers have no association with each other: Amber (Tara's girlfriend) and Judy Hicks.
Sidney getting attacked at the beginning was a rejected idea for Scream 4. And the whole "killer who has no connection to the other killer(s)" thing was supposed to happen in Scream 2 and maybe even the original Scream 5.