Except we might already have those in the unmodded game. If not, though, putting a Nord somewhere in the game and not giving him any clothes shouldn't be too hard.

But I'm sure we'll see ridable dragon mods at some point. I mean, there's already dragons in the game, assuming we also have mounts, I'm sure someone at some point will find a way to make dragons ridable. Even if functional mounts don't make it into the finished game, I'm sure someone will find a way to make them work, it will just be harder, and the results possibly less polished if it's not part of the original game, after all, there are mods adding functional mounts to Morrowind. Still, whether mounts are in or not, having dragons already in the game will likely make creating ridable ones easier, seeing as the game would already have the animations and models for them, and already be designed to handle a creature like a dragon.

Though, I suspect I wouldn't download such a mod myself, nothing really against the idea, it's just that riding dragons isn't something I particularly feel I need to have in my game, especially with the dragons appearing as the main enemies in Skyrim. It would just seem rather degrading to dragons to ride them, it would be like if someone made a mod for Morrowind that let you summon Dagoth Ur and have him effectively function as a glorified Creeper. But people can make whatever mods they want to, if someone makes a mod that doesn't interest me, I just won't download it. It's pretty simple.