Life's not easy when your name is Bran Stark. The poor kid is thrown out of a tower window in the pilot episode of Game of Thrones, and by season six he realises he's the cause of his best pal's "Hodor"-ing. It's about time something nice happens to him, and that's why we think the "Bran is going to warg into a dragon" theory is an excellent idea. He may never walk again, but that doesn't mean he can't use his nifty abilities to be an integral part of the battle to come! (Besides, if the Night's King's touch leads to Bran breaking the magic that prevents the White Walkers from crossing the Wall, as many fans believe it will, then he's definitely going to be jonesing to play an active role in the Great War.)
Reddit user harvey-spector offered up a concise argument about why Bran soaring through the sky in the form of one of Daenerys's dragons is totally plausible. It all goes back to the Three-Eyed Raven and his promise to Bran that though he will never walk again, he will fly. Now, there is a legitimate argument to be made that Bran's mentor means he will fly through time. Thanks to his greensight, Bran is becoming adept at moving both forward and backward in Westeros's timeline. He's flying in a metaphorical sense, but there's no reason the Three-Eyed Raven's words can't be literal as well.
"With all signs pointing toward Jon and Daenerys meeting this season to work out an alliance in hopes of dealing with the undead army heading their way, Bran is finally in the perfect place to join the battle."
As harvey-spector notes, in the scene where he promises Bran he will fly, the Three-Eyed Raven clearly wants the Stark boy to realise the full extent of his powers. Even though Bran will never regain his ability to walk in his own body, his potential to live a full life is limitless. He has gifts other people can only ever dream of having. How he chooses to use these gifts will be telling.
The Wylis incident should serve as a warning to Bran that he needs to learn how to fully control his powers. Since he has lost Summer and Hodor, Bran is in a position where he can't simply warg into one of his companions whenever he wants to escape his own body or take part in a fight. Unless the White Walkers immediately follow him into Castle Black, Bran should have at least a little time to practice warging into animals with whom he doesn't have a close connection. As he grows into his abilities, his confidence should grow as well.
By the time he reunites with Jon and has an opportunity to meet Daenerys, he could be ready to take flight — literally. Having Bran warg into a dragon isn't just a flight of fancy; it's a wise strategic move. Daenerys's children are as unpredictable as they are deadly, and if Euron Greyjoy is in possession of Dragonbinder, then she could lose control of them entirely. This is where Bran comes in. By entering the mind of Drogon, Bran could potentially turn the tide of the entire war and bring the dragons back under the control of the Dragon Queen. If he takes control of just one of the dragons, he could feasibly break the magical hold Euron may have on them. It's a clever loophole the show should exploit if it does introduce Dragonbinder in season seven.
Giving Bran's powers a role to play in the show's end game, beyond his ability to time travel, would be rewarding on so many levels. He spent his childhood in Winterfell always climbing closer and closer to the sun. Now, even though he's lost the use of his legs, he's one of the show's most powerful characters. It's time for him to show the people of Westeros what he can do, and if would be amazing if he does it by breathing fire on an army of White Walkers.
This is one theory that's not a game changer on a massive scale, but it could provide Bran with a fist-pump-worthy hero moment. And if anyone deserves one of those right about now, it's Bran "everything-I-touch-turns-to-crap" Stark. Let's give the kid a win, shall we?