I'd like to see this in Skyrim as well. It's one of those things that might seem small to some, but in truth really goes a long way to making a first person gaming experience seem more believable, and honestly, I really don't see why more games don't do this. I mean, if done well, it really doesn't get in you're way much so it doesn't really detract from the game, but it can certainly benefit it.
The trailer though doesn't really tell us whether it will be in the game or not, as the player never looked down far enough to really show us whether the body is visible in first person. The bit with the hands stretching out when the player almost fell off the cliff was nice, but lots of games which don't feature first person body awareness have shown the players' hands even when not holding a weapon.
Considering in the average first person game you are focusing on what is in front of you, not under you, I really don't understand the persistent obsession with seeing your own feet. Can someone explain this to me?
While usually you're eyes will be focused on what's in front of you, you will at times have to look down, and it looks kind of awkward when every time you look down you're reminded of the fact that you're not playing as a person but rather a floating camera with a pair of arms attached, that's as good a reason as any to add it if you ask me.