Whilst replaying Portal recently, I was again struck by the game's highly interesting, and entirely optional, developer commentary. For those who haven't played it, you can play through the game again once you've beaten it, this time hearing audio commentary by the game's developers about your immediate surroundings- the reasoning behind certain design decisions, and all sorts of interesting background information. How cool would it be to have this in Skyrim? You could be on a mission, when suddenly that mission's game designer starts talking about the mission's development; or you might be in an ice cavern, when an artist decides it appropriate to wax lyrical about the ice walls that he is responsible for; or, after casting a spell, the game's sound designer could very well begin talking about why the spell sounds the way it does, and the complicated processes involved in coming up with a two-second sound effect.
I know that this is pretty superfluous stuff, and that our main concern is that Skyrim is as good as it can be. But some sort of director's commentary, in the manner that it is performed in Portal, or some other commentary system, would be really, really cool.