If your not familiar with NV hardcoe mode basically it added weight to ammunition, and required you to eat,drink, and sleep. So pretty much like a Realism mod included into the base game as an option. Personally I hope Bethesda includes this as well for Skyrim. Some may say it isn't that necessary as mods will surely add this stuff. But that doesn't help console players, and it would be nice to have it in by default with an achievement for beating it.There is some additional stuff I would like to see be a part of it as well. I would like:
No Waypoints on compass you have to find stuff yourself like Morrowind.
Darker Nights an Dungeons. You really need to use Torch or light spell to see if caught out at Night.
If Vampirism is included again make it more deadly to be out in the sunlight.
An of course the NV stuff like realistic weight on all items an need to eat,drink, sleep.