I have Skyrim on the Xbox 360 and don't own a PC that can do it justice. Nonetheless, just for kicks, I have been thinking about what kind of mods I would like. This is one of them.

Sleepy Time Mod

Failure to get sleep results in negative status effects.

• After 12 hours without sleep, the player becomes 'Tired': a 20 percent reduction in attribute regeneration and skill learning.
  
• At 18 hours, the player is 'Sleepy': a 40 percent reduction in attribute regeneration and skill learning; and a 20 reduction in maximum attributes.
  
• After 24 hours, the player becomes 'Exhausted': an 80 percent reduction in attribute regeneration and skill learning; a 40 percent reduction in maximum attributes; and vision responds much slower to changing brightness.
  
• At 48 hours, the player is 'Delirious': attribute regeneration and skill learning cease altogether; maximum attributes fall by 60 percent; vision responds much slower to changing brightness and randomly blurs; left- and right-hand buttons swap randomly; and players begin having auditory hallucinations, e.g. dragons swooping, innkeepers talking, arrows zipping past, or bandits making threats.
  
• Finally, after 96 hours (4 days), the player collapses: they sleep for 12 hours and wake up 'Tired', with a 50 percent chance of having items stolen in the meantime; they die if the collapse occurs while in combat or enemies are nearby.

Every 4 hours of sleep rolls back these effects one stage. Therefore, a 'Tired' player will need only 4 hours of sleep to remove all penalties, while a 'Delirious' player will need 16 hours. A positive status effect is earned by getting 4 hours of sleep in addition to whatever is needed to remove all negative effects. These would work similarly to the existing positive status effects, but with added benefits, that each last for 8 hours.

• Sleeping an extra 4 hours earns the 'Rested' bonus: a 10 percent increase in attribute regeneration and skill learning.
  
• Sleeping an extra 4 hours in a bed owned by the player gets the 'Well Rested' bonus: a 20 percent increase in attribute regeneration and skill learning with a 10 percent increase in maximum attributes.
  
• Sleeping in a bed with or near the player's spouse earns the 'Lover's Comfort' bonus: a 30 percent increase in attribute regeneration and skill learning with a 20 percent increase in maximum attributes.
  
• On the other hand, sleeping too much, perhaps 8 hours more than necessary, will result in a 'Lazybones' status with minor negative effects, e.g. the same as 'Tired'.

I imagine most of these features would be relatively easy to mod. Most likely, the difficult effects would be the visual impairment and auditory hallucinations. There would need to be some way to change the speed that the camera's "eye" adjusts for different brightness conditions; there would also need to be some way of jury-rigging Bethesda's blurring effect for this alternate purpose. The auditory hallucinations might be the hardest thing, though, especially if they are to sound like they are coming from within the world, e.g. echo in caves, sound distant, or come from a particular direction. I suppose it would also be difficult to get the left- and right-hand buttons to swap randomly. However, nothing above introduces new content, but instead just adapts existing systems to create new features.

New content that might complement a mod of this kind mostly comes in the form of additional food, ingredients, and cookng recipes.

• Coffee beans. Effect: rolls back one stage of sleep deprivation for 4 hours, upon which the player reverts back to their previous state. They are not a substitute for sleeping, but merely offer a temporary relief.
  
• Sugar pile. Effect: restore 5 points of health.
  
• Flask of coffee. Cooking recipe: coffee beans (1) and sugar pile (1). Effect: rolls back two stages of sleep deprivation for 4 hours, upon which player reverts back to previous state. Not a substiture of sleep, but a better temporary relief than from coffee beans.

Coffee beans and sugar piles could also be made into ingredients for use in alchemy. I doubt creating these items would be particularly difficult. There are probably some existing ingredients that could be retextured to look like coffee beans, and the sugar pile could just use the same model as the existing salt pile ingredient. Another new item would be a portable bedroll to use in the wilderness, but without the potential of getting positive status effects. Using it would also come with a small chance (maybe 5 percent) of being woken by an attacking animal or bandit, or having items stolen by a thief.

I estimate that Skyrim would be about 0.2 percent better with this mod.

EDIT: http://www.gamesas.com/index.php?/topic/1301995-rough-design-for-a-sweet-dreams-mod/ for another mod which would complement this one nicely.

I'd use this mod.

Like the idea. But coffee beans and sugar piles makes more since as cooking ingredients instead of alchemy ingredients.

Some alchemy ingredients are also cooking ingredients, like the salt pile, so coffee and sugar could be both. Supposing this mod existed, some people would probably wonder why they can't use coffee and sugar in alchemy, and since doing so wouldn't prevent them from also being used in cooking, there is little reason not to make them alchemy ingredients too. In any case, it wouldn't be a big detail, which is why I phrased it like a suggestion.

Good point.

You could also add other ingredients and recipes it later on.
ingredients
raw sugar
roasted coffee beans

cooking
candy
coffee cake
roasted coffee beans-ingredient
espresso