It seems that the carriages, or at least the horses for the non-intro carriages are not the same; they aren't 'proper' horses (you can't kill them for example, and if you set a path for them they don't walk, they hover. They also aren't actually connected to the carts). Hopefully it shouldn't be difficult to find and rectify these differences once we have the CK.
I've managed to re-path the carriage from the intro cutscene (messily, using the console/Script Dragon) and the horses pull the carts along fine, though the pathfinding isn't exactly fantastic and the cart tends to tip over... I haven't tested over long distances though, I'm not sure if it would be better or worse, the AI have a tendency to cut corners on the roads which with a cart isn't going to be so good.
EDIT: I went on a slightly longer journey, ran into bandits. Apparently you can die despite not having an actual body at that point in the game.
Based on your findings though do you think it is a realistic idea to have carriages carry people across Skyrim?




I just came to post that here, didn't realise it was a dev though. I'm curious to see what happens when you run into enemies.