No Magicka - It would be great, whie playing a pure Thief or Warrior type to have no spells at all and no Magicka displayed on screen. Sure, I can choose not to cast spells, but I'd prefer them to just not be there at all.
A choice of only ONE of Alchemy, Enchanting or Blacksmith.
Armour limitation. Heavy only, Light only, Cloth only.
Weapon restrictions.
And, of course - Dead is Dead. With a big warning and several "Yes, I understand, I won't complain when my character dies!" confirmation buttons.
There could be more, but that's a good start.
Note - these would be choices, not enforced on any character and with no associated bonuses to encourage players to choose them if they didn't really want to. More for role-playing and for players who can't resist creating incredibly powerful characters but then find the combat a bit easy.
Playing a stealth character, I'm completely avoiding magic, smithing and enchanting. Even with sneak maxed out, the game is never so easy that I feel overpowered. I know that I could create some incredible gear, but I'd rather not do that... although I could. What would be nice is if I was able to choose these restrictions as permanent options at character creation.
If anyone is working on a Mod to do this sort of thing at character creation, I'd love to know about it!