I can understand having come clumps of hair or clothes that move, but you just need to consider a few factors of how it would work in Skyrim.
1. It can't look bad when looking at someone in first person. In native third person games, it's easy to have systems like this where it doesn't have to be perfect, because the camera is zoomed out and you can't look at finer details. But Skyrim does have first person, and you have to make it look natural.
2. There are many video games that have good cloth and hair physics (such as Assassin's Creed, noted above). However, playing Assassin's Creed, one must consider the extent to which they are implemented. There are main characters, who look nice, while generic NPC's don't have any unnecessary physics. In Skyrim, there will be NPC's all over the place wearing the same clothes you are, the same hairstyle you have, so you need to have the detail on everyone, not just the player, be equitable. That detail can't be so good it lags the game.
3. These systems, when coupled with other systems, can't make the game laggy. Skyrim is trying to do a lot already. The system of snow, the water, the shadows, and the advanced lighting all contribute to performance demand. There is an edge to this bucket, and we don't know how full it is. Adding another system on top of it can make it overflow, and it might not be able to be included without making another system worse.
That's about it I suppose. I'm just hoping that, if it's not included, it can be modded in on the PC version. Havok controls animations now, so hopefully we won't have the problem in Oblivion where parts of characters can't be havoked because of the animation system. At least Skyrim is still an improvement, where long hairstyles such as the ones provided by Ren could only move with the head, and loved to float or clip based on where your head was angled. Now that they angle with the body as well, we can at least have some long hairstyles that don't look ridiculous