I restarted the game and watching again the intro movie a thought came to mind: is this a scripted cutscene or is it the real engine handling those carriages movement? Because everything seems in-game real, the horseman, the people in the village. And I payed attention to the carriage "pathfinding" and seems pretty accurate. So if the game engine allows this, why aren't the paid carriages actually moving like the ones in the intro?

It would be so much more in the spirit of the adventure to actually do the whole ride and get off whenever you want, even shoot arrows to the wildlife without getting off, or be attacked by random bandits, or attack caravans yourself. Static carriages with loading screen is a wasted opportunity in my opinion, I mean Morrowind had this 10 years ago, where's the progress? There could always be a "skip to destination" button if you wish so.

Of course it is, since a mod does it.

Yeah I wish the carriages and the boats moved on the map, the world would feel more alive. It was clearly not the devs' focus this time. The horses improvements are barely visible (I'd even say they were better in Oblivion with 1st person) and I guess they added carriages at fans request, a lot of fans asked for paid transport like in Morrowind as an alternative to fast travel. Red Dead Redemption pulled nice carriage rides, and Todd mentioned that in an interview, so I guess there's a good chance they improve the transport and make it real in the next game.