Like the idea of compass/map, etc. becoming in-game items (the compass was in-game in Thief, the map kinda in-game in Far Cry 2, and it was nice in both cases). Minimal HUD, too, which is nice for immersion.
For the magic quest marker, in hardcoe, it should be a literal magic quest arrow; that is, you could get a blessing from a priest of Talos, e.g., that would apply the magic compass to a specific quest, for a day or so. It shouldn't be a map marker, though, just a grail-like beacon in the distance in your mind's eye.
Prefer ambushes with fast travel and resting -- but as part of normal play, not hardcoe mode.
Like a food/drink/rest mechanism, but not too over the top. Some sort of tax on character time to encourage players to use it strategically and experience some of the concerns that a real adventurer would deal with (i.e., scraping together enough money to pay next month's rent -- don't laugh, it was a decent catalyst for Garrett's adventures, after all). Also forces characters to use some of their inventory space for packing and storing food -- getting a backpack full ancient gold does you no good if you starve on your way back to town.
As for die rolls, I think it should really cover (in melee) your chance to hit the weak points in armor and on the body, rather than affecting damage directly and consistently, or causing you to miss Morrowind style. It could also affect blocking or counterattacks or successfully pulling off maneuvers more complicated than "hit thing with sharp thing". Regardless, it's not realistic to have a completely separate system for a hypothetical hardcoe mode, so this preference applies to normal mode too.
Injury System: Like spell effects or disease; most wounds from falling or battle should inflict an "injury" of some sort, which would usually involve some health and stat penalties, maybe some special conditions like nausea or spell failure, etc. Injuries would make it harder and harder to fight and avoid further injury, until eventually you're incapacitated, at which point you're captured, slain, or left for dead. Health would still exist as a number, but would be less about wounds and more a measure of general condition (thus, very affected by food, water, rest, and disease as well as injury and blood loss).
Disease should not only be harsher and potentially fatal if untreated, it should not be as easily curable -- Disease should have a magnitude (call it "virulence"), and a Cure Disease effect of that magnitude or greater should be required to treat it. While disease should lower health, high health should contribute to resisting disease in the first place.
Agree with object weight -- however, the game economics should be centered around more traditionally adventury forms of loot -- ancient artifacts and writings, massive jewels, caches of coins, trophies, magical items, and so on. Note: All things that are fairly small, individually. You shouldn't even be tempted to bother with the hassle of strolling into town and pawning a hundred sets of dented up iron armor. In fact, no one in town should be willing to buy a hundred sets of armor from you. Craftsmen should sell the product of their labor, not resell the finds of adventurers. Finding armor and weapons should mainly be about either upgrading and keeping nice equipment, or maintaining a more... cinematic playstyle that involves abusing your weapons and then grabbing more weapons off the ground and wrecking them too. Armor should mainly be valuable for upgrade or replacement parts.
If the game takes place in Skyrim, one other hardcoe feature to consider: heat management. Once you leave warm areas, your body temp would start dropping. Argonians are susceptible, Khajit are resistant (for reasons that are hopefully obvious), as are Nords. Clothing/leather is good for slowing heat loss, metal is as useless as walking around naked, fur is great. You find or build fires to help recover your heat, and mages can use very subtle, controlled pyrokinesis to keep themselves warm (or they can blast their enemy to cinders and warm their hands over the embers). General area temperature would vary with place, time, and weather conditions, but cold and heat effects (including fire and frost magic) could provide short-range boosts or penalties. Water in particular would be promote hypothermia. Hypothermia would sap health, but would also affect penalize agility as you start to shiver uncontrollably.