What would you want it to exactly? Like details.
Cheers
Personally (Though this was directed at the people who answered so far...), I would like to see Tiredness, Hunger, and Thirst implemented. The issue I see though, would be if it would have health items regenerate health like New Vegas... since magic is suppose to heal all wounds and whatnot.
if we could get some sort of bodypart damage system in place it would make more sense, because healing wounds... you would simply have more choices that do the same thing, and would allow for greater flexibility in RPing and character development... while something like a broken leg (No I'm not using the obvious joke here), would need be treated by a doctor NPC or something.
The more I type and think about this, the greater of an undertaking it seems like it would be though, considering the system in place would make anything beyond just the essential needs of a person, difficult to implement.
And to address this:
Having to eat and drink to regen health and magicka perhaps.
But hardcoe mode similiar to fallout is kinda pointless for this game.
Skyrim is not a post-apocalyptic nuclear wasteland. The water is not irradiated and food is bountiful. It is much too easy to live off the land. There are even snowberries that grow in the tundra.
New Vegas' hardcoe mode wasn't exactly impossible either. Kill some Coyotes and your set just as long as you svck water out of enough toilets.
You mention Magicka regeneration above... that wouldn't be bad. Maybe greater magicka volume, but it can only regenerate through... meditation or something, so using spells means you have a fixed period until you burn out and can't use any prior to drawing more power from the ether or something.
Do we have any available information of what exactly Magicka IS? I mean is it Mana, or is it the amount of energy you can channel at that time?