I hate the idea of hardcoe mode, as this isn't Fallout. People who live in Skyrim would likely know how best to survive there and it wouldn't be like a constant threat of demise. Plus, hardcoe mode wasn't very hardcoe. It was more chore than anything. Once in a while I had to stop and wade through a menu to eat one of my 86 food items or pure waters that I literally never ran out of once. Ammo had weight, but it wasn't heavy enough to make my drop much of it, and I'd just stockpile it at my house anyway.
hardcoe mode in NV wasnt very well implemented but there are plenty of ways to implement a fun and meaningful hardcoe or Survival mode in Skyrim.
First, get rid of fast travel and instead bring back a system similar to the stilt striders of Morrowind that for a fee will allow you to travel quickly between towns, fast travel and hardcoe mode just dont mix, when your character is in the middle of nowhere and starts to get hungry, tired or thirsty and you dont have a bed nearby or food in your pack it is a little cheesy that you can open up the map and teleport to the nearest town, use a bed and stock up on supplies then head back out again with no consequence, if fast travel is removed and the character is out the middle of nowhere with no supplies it forces the player to live off the land and find shelter wherever he can and this is really what a hardcoe/survival mode should be about.
Second, give some foods an expiry date. In New Vegas it was all too easy to load up on supplies at one town to last you on your trips between towns, the sheer abundance of food available made sure that your character would never go hungry and made foraging for food unnecesary, give food an expiry date in Skyrim and it sort of limits the amount of food you can carry without most of it going to waste, sure you can stock up on food for trips between towns however if you plan on spending a long time in the wilderness you will have to hunt and forage food yourself to survive.
Third, have the weather and climate play a role in your fight to survive. We all know Skyrim is a cold place so it would be pretty cool to see certain areas and nights have a negative effect on your stats unless you wear suitable clothing to keep the warmth in. If you want to take it furthe you could also have snowstorms and blizzards kick up at certain times that force your character to find shelter lest he freeze to death.