#1 The Fiend's streak doesn't have to end

It's no secret that no one wants The Fiend's undefeated streak to end at WrestleMania 36 and WWE shouldn't allow it to. Either that or face resentment from a fanbase that is completely enthralled in the character, which is why a match with John Cena is such a great idea.
Think about it this way: Cena versus The Fiend at WrestleMania allows the company to have the best of both worlds and start to blur the lines in the process. For example, in a storyline, everyone always expects good to overcome evil, which is why the opposite happening would be an absolute shocker to fans.
Secondly, not ending The Fiend's undefeated streak allows for the company to keep the lore going past WrestleMania and keeping the character on top. If nothing else, that seems to be what the WWE Universe wants right now and anything less would just feel like a disservice to everything the company has achieved with The Fiend.