Speaking of the guy in question, he is on a really important mission with Meera to inform his brother about a mis-parentage case. Now this theory about Bran comes from the fact that he can create ripples in past which impact the present, firstly with Hodor and then at the Tower of Joy when he calls out Ned and he seemingly hears his future son's voice.
So according to this theory, Bran will become an integral part of the story as the series nears its end and there is a possibility that many of the things in present have been the result of these ripples Bran created. So, we have the Mad King Aerys who heard voices and it is possible that our little guy here might have had a role in that.
In what will be the craziest of them all is the possibility that Bran is, in fact, all the Bran’s in the history of the kingdom. Remember Brandon the builder? In the books there’s this passage recited by Old Nan which explains it:
"I could tell you the story about Brandon the Builder. That was always your favourite. Thousands and thousands of years ago, Brandon the Builder had raised Winterfell, and some said the Wall. Bran knew the story, but it had never been his favourite. Maybe one of the other Brandons had liked that story. Sometimes Nan would talk to him as if he were her Brandon, the baby she had nursed all those years ago, and sometimes she confused him with his uncle Brandon, who was killed by the Mad King before Bran was even born. She had lived so long, Mother had told him once, that all the Brandon Starks had become one person in her head.”
And then there’s the possibility that when the three-eyed-raven tells Bran that he will never be able to walk again but will fly instead, what he could actually be implying is that Bran will turn into one of the dragons?