There should be negative effects for staying up too late. After 10:00 pm your vision might start to get blurry, and every hour the blurriness multiplies by three, and once it get's to the point where you can't even see, you pass out. Once you wake up the time is set to have your vision blur after 16 hours, so you can change it by staying up longer/shorter.
It all depends on your sleeping habits. With New Vegas' hardcoe mode I wouldn't put something like this as to far off.
On to other things.
I just thought about bows. I find it a little difficult manually aiming.
I don't want manual aiming abolished, but if they could implement an Auto-targeting system. Like the kind seen in the Legend of Zelda games(sorta like VATs but in real time).
The advantage would be easy targeting of moving enemies.
And the penalties could be no head shots.
Another thing about bows, is enviromental effects. In Oblivion and Morrowind the arrow shoots in a straight arch from the bow. But the weather effects and Skill of the player should effect that. Wind should push it off to the side, and if the players skill is really low there should be missfires.
As opposed to fatigue draining, 30 seconds shall pass before the arrow has to shoot.