It has to be nigh-impossible to create a realistic underwater swimming animation!
As a person who's done some animating
Underwater:
1. You'd have to account for the natural bobbing/buoyancy of the human body.
2. You'd have to account for the fact that in the water we are no longer limited by gravity, nor do we have to worry about falling, which means a huge degree of freedom of movement, meaning there would have to be a whole new movement mechanic in which you'd spin accurately and turn towards wherever the camera was pointing.
3. People can swim upside-down, turned 90 degrees, from side to side, twisting and winding all over the place, etc.
4. Everyone has a very different style of swimming. I've been told that the way I twist and move around that I look pretty graceful in the water, as compared to a person who just powers through it. I even do dolphin kicks.
5. Getting hit underwater is much different than getting hit into the air, go farther, but it also hurts much less, the ragdoll would hypothetically have the arms and the legs go out opposite to the direction of movement, as would the whole body, unless there's a specific animation in which a person stayed rigid instead of going ragdoll.
Above Water:
1. See Above.
2. See Above.
3. See Above.
4. See Above.
5. People have different methods of swimming, in there's a specific Japanese style in which people nearly silently swim, and it was used for stealth. So if they're going to be going all-out they'd probably have to account for that.
Other things to consider:
There are no diving animations and a diving mechanic would require a whole new conditional formula to find out how deep the water is, how far you are above the water, if you could realistically make it, and how quick/slow to make the diving animation.
People slow down when entering water much quicker, but it isn't like Oblivion where you're right below the surface if you jump off something 20 feet above, if they're going to be going for all-out realism, they'd have to consider that.
Don't even get me started on how armor, clothing, and other things would be in the water, it'd be a nightmare to figure out buoyancy and how much something should way in-water compared to out of water. Hair, if given physics, would be a nightmare in water. (although, really, you'd just have to make it Zero-G and give it more rigidity at the roots to make it sort of "puff out").
Some weapons won't work in the water. You can't honestly say that you could murder somebody easily with a hammer underwater.
Weapons and Armor would make you sink if you lifted them above the water. Just a fact.
I could go on but I'm getting very bored.
All I wanted, personally, was a system where the body moved realistically and clipping was minimal. Don't care if it's a uniform style of swimming for everyone or if diving isn't in the game. Buoyancy isn't an issue to me either. Would be greatly appreciated in the future but not a necessity.
It differs here because (Pay attention, this part is important.) I don't go making threads complaining about anything. Really I just chose something that I may be a little tiffed about but really I don't care that much about no spell creation being in Skyrim. I was really just trying to make my post relate to most of the complainers out there by stating "Hey I'm a little upset about this but you don't see me making threads to complain about it because in reality it's no big deal" I probably should have just typed that in the first place. My bad.
Are threads that valuable to you? This is a place for discussion. If you don't like it, leave. It's that simple.