In Two Worlds, you can move the camera and character around, but once you reached a certain distance, the character is forced to turn back and face the NPC he's talking to. I would like that in Skyrim.
I did only assume that the PC was locked in place during conversations because it was the only thing that made sense : if you move about and you end the dialogue, it could rank from annoying to problematic - if that's one of the important dialogues you can't always start back.
A system as you describe would be more natural, while preventing that. It sounds much, much better.