I like this idea, I have actually thought about doing something like this in the past. Its funny actually because when i described Half-Life 2 to my sister one of the first questions she asked was "so you can look down and see your feet?", obviously i said no, and she replied with "ah well that would have been cool".
As the source engine is going to be used for the next version if this was actually to be used there would be a problem as the users player model isn;t actually rendered at all, so that would have to be changed. would be definatly worth giving it a go at least
It used to be rendered on the old HL1 engine though. Would be funny if you could shoot your own feet and end up killing yourself, haha would be a fun new way of suiside