Someone should actually try and get Bend will before finishing the Vanilla MQ and then go try and Ride Alduin. I doubt it would work but who knows. Maybe use Dragon Aspect, a Amulet of Talos, and Blessing of Talos, then Dragonrend Alduin to bring him down and make him vulnerable, then use Bend Will and try and ride him lol.
It doesn't work.
There are a few dragons which just the Player can't ride.
I've mentioned this in another Thread somewhere, but there's about 5 you can't ride.
Paarthurnax, Alduin, Skeletal Dragon in Labyrinthian, Durnehviir... forgot the last one, but basically the ones that you can have a chat with are the ones you can't ride. Although... I believe you CAN ride Odahviing. (
sorry for the spellings of the Dragon Names).