#3. Unannounced John Cena or Undertaker match
We are facing the prospect of a WrestleMania without either John Cena or Undertaker wrestling in a match. I can't remember the last WrestleMania that happened without featuring either Superstar, but at the moment the sixteen match card doesn't feature them.
Now there are obviously rumors that both Superstars will actually be doing something at this year's show, perhaps they'll be challenging Kurt Angle after his match with Baron Corbin. Perhaps they'll interrupt an Elias performance, perhaps they'll wrestle each other again.
Either way, despite being slightly expected, an actual match on this year's 'Mania card from John Cena or Undertaker would be a surprise that people wouldn't have thought would happen, especially given the number of matches on the card already.