....I can only imagine "full body visibility" combined with some of the body mods that have been made for OB/SK/FO3. You'd never be able to see your character's legs.
(Oof, and combine that with any of the "bouncing" mods.... )
Hmm, wonder if it would be possible to mod OUT a visible first-person body if they made the mistake of putting it in?
edit: more seriously, I can only imagine that view & some of the outfits (hugely bulky armor, full rad suit, mascot outfit - although we've only seen a head so far, etc) not combining well. Would also say Power Armor, but they've made that a vehicle not an outfit....