His visions in the show weren't just of the past. Some of them clearly weren't. The shadow of the dragon flying over what looked like King's Landing for example, or the ruined throne room covered in snow (I guess one interpretation would be he is seeing Dany's previous vision but it could also be he is having the same vision of a possible future).
One interesting thing about the dragon vision. It never shows the dragon itself. Could it be that Bran eventually gains the ability to warg into a dragon, even from great distances, and the vision is what he one day sees through the dragon's eyes?
Will the rotting horse end up being Cold Hand's mount? (I know it was an elk in the books but that's something I could easily see them changing for ease/expense of shooting).