WrestleMania, traditionally, is not the domain of the shocking moment. WWE creates certain expectations, and more often than not delivers upon them to provide fans with the happy ending elusive to the other 364 days of the year.
You're going to see a hard-earned babyface World Title triumph. You're going to see a major finisher kick-out, as opposed to the minor ones you see five times on every episode of Monday Night RAW. You're going to see absolutely ridiculous attire. You're going to see at least one genuinely awesome pro wrestling match. You're going to see a slow and methodical Triple H match bereft of heat and a half hour in length. You're going to see an André The Giant Memorial Battle Royal winner plucked from a hat and sent right the f*ck back to obscurity.
And so on.
That said, in recent years, WWE has delivered the shock usually synonymous with the "RAW After WrestleMania" which, incidentally, you cannot believe walking brand Stephanie McMahon hasn't found a way to market more effectively. Last year, the Hardy Boyz returned, and Goldberg actually wrestled for longer than a Primo Colon sighting. Two years prior, Seth Rollins burned down the grand coronation of Roman Reigns.
And, since 'Once In A Lifetime' means nothing to WWE...