#3 Kevin Owens cashes in the contract
Here's a possibility that you might not have considered yet. Kevin Owens could win the contract from Braun Strowman earlier during the night. And then, when Roman Reigns and Brock Lesnar have knocked each other out, he could cash his contract in. This would make him the first ever 2-time Universal Champion.
Expect the wily veteran to pull some dastardly tricks when the main event of SummerSlam is underway.