#3 The WWE Championship changes hands

Well, one match being advertised for the event is WWE Champion AJ Styles vs Samoa Joe at the 1,000th edition of the show - and what would be bigger than the main strap changing hands?

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Joe, of course, has a shot at the title at SummerSlam - so it could very well change hands before October, but I predict that AJ Styles will retain at SummerSlam, and Joe will get his rematch and walk away with the gold at SmackDown 1,000 - mirroring Styles' win over Jinder Mahal when SmackDown rolled into London last year.
Needless to say, this card, as always, is subject to change - so it may not even be Samoa Joe who faces AJ Styles on the show, and the match set isn't confirmed to be a title match. Even if so, it could be a dark match, which wouldn't be unusual. To have the title defended on the show, though, would be huge, and to have it change hands would be monumental.
This could be huge.