I proposed an idea like this in the "hardcoe Mode" thread, albeit as part of my suggestion for modular realism options. I also suggested that potions/spells/scrolls that offer "frost resistance" would be helpful-and of course just being a Nord would be helpful (I think the one person who mentioned that to be bad meant that it would seem to "unbalance" the game, but since the whole feature would be optional anyway I don't think that matters). Other things the player could do is set up a camp fire, perhaps find shelter in a cave of cave-type area or set up some kind of tent or something. How much damage the weather does to the player would be determined by the difficulty slider, along with how much clothing/armor they're wearing. I'f you really want to run around naked I'm sure there'll be a mod where you can get an enchanted bikini with a 100% frost resistance constant effect.
As for not being able to swim with heavy armor-I think that would make sense as well-again perhaps as a "realism option". It would also be nice if the CS were set up in a way where a user can actually add such elements to the game-like a new option in the options menu. It would be pretty nice if the Skyrim CS gave us the ability to do things that we'd probably have to hack into the hard coding of previous Elder Scrolls games to achieve-but that's, well, a little beside the scope of this thread-although I'm suggesting it simply because if Bethesda doesn't include things like this in the game, the least they could do is give us the ability to somewhat easily implement these sorts of features ourselves.