#3 John Cena could have turned heel after ending The Undertaker's Streak
One of the biggest missed opportunities of John Cena's WWE career was that he never turned heel after becoming a major star. He nearly did so in 2012, playing the default bad guy in his program with The Rock. A heel turn shortly after the event would have done wonders for Cena and the general WWE product at the time, with The Undertaker possibly playing a part in it.
The one issue with a Cena heel turn was that the fans so desperately wanted it, which meant that he would likely be cheered upon becoming a villain in WWE. That would have been solved if he turned heel by defeating Undertaker at WrestleMania and ending The Streak.
It would have served up astronomical amounts of heat for John Cena, having taken away one of the most beloved things in wrestling history. Needless to say, a full-blown WrestleMania program between Cena and Undertaker would have been absolutely massive.
Imagine if the 16-time World Champion cheated to end The Streak. The heat would have been nuclear, coming from all sections of fans. It could have featured two of the most shocking moments in modern WWE history, both taking place at the same time.