The fan theory: Neville was the real Chosen One all along
I know, I know. The prophecy could've been referring to either Harry or Neville, but then Voldemort had to go and mark Harry as his equal, like some kind of moron, setting into motion the chain of events that would lead to 1) his own demise and 2) the travesty that was Harry naming his son Albus Severus. I KNOW ALL OF THIS.
But how very, very cool would it be if, during the Battle of Hogwarts, Harry attempted to vanquish the Dark Lord and wasn't able to pull it off? And then Neville—timid, talentless Neville—steps in and delivers the final blow? Remember how we all felt when Neville got ten points for standing up to his friends and won the House Cup for Gryffindor? This would be like that, multiplied by a thousand.
The Harry Potter books are all about choices. “It is our choices, Harry, that show what we truly are, far more than our abilities.” Harry CHOSE to be in Gryffindor. He CHOSE to take down Voldemort or die trying. We’re told the prophecy had no bearing on his choice, but if Harry chose a destiny that didn't actually choose him—if the Chosen One wasn’t really the Chosen One at all—it would have really driven the point home.
And—look, I get it, I’m rambling on a bit and you probably have places to be, but just stay with me on this—what if Dumbledore knew all along? What if he was singling Harry out as the “Chosen One” to keep the spotlight off Neville?