#4. Ronda Rousey interferes during Becky versus Charlotte
Charlotte Flair will face Becky Lynch at Fastlane, with Lynch getting added to the RAW Women's Championship at WrestleMania. This match could end in a no-contest as per WhatCulture. The most obvious reason WWE would book a no-contest would be to elongate the storyline and to keep Charlotte looking strong in the run of the Mania.
If WWE does decide to go with a no-contest finish, the best way would be for Ronda Rousey to interfere and attack both women.
#3. Dean Ambrose turns on Roman Reigns
Another big surprise that can happen is Dean Ambrose turning on Roman Reigns, although I will admit its a little unlikely.
If Ambrose is still leaving, WWE can use him for one last big WrestleMania match against none other than his best friend in real-life, Roman Reigns. The only reason Ambrose will turn on Reigns if this is the match planned for Reigns at Mania because we know he will wrestle now that he's healthy again.