"What does it add to gameplay?"
Consider the hedgehog appearance of early glass armor with silly looking spikes all over. Without cloth based systems you either have to make a cape model for each of the armors, or a complete upper body replacement for each combination. With cloth physics, you just define the hardpoints a cape connects to and let physics do the rest. Daggerfall allowed all kinds of combinations as it didn't have to worry about the 3D model or animation aspect. Cloth would allow the same thinking process in 3D, so thus it would be more feasible to have "capes on everything and make it look good". Rather than making it impossible due the number of models that would have to be made using a modeled approach.
So it affects gameplay in that it would be possible to have certain things in the game without adding a tremendous cost to models. It adds to gameplay in that capes would be there instead of left out. Clothing and armor combination systems haven't exactly *improved* with each game since Daggerfall...
you seem to have the impression that the rig that would allow for cloth sim is somehow not
very specific to the model itself, Besides the collision shapes, that act as colliders that will simulate the body under the cloth, the cloth itself has a rig set up so that it can be moved/physicized at all.
As I understand it, the cloth bones have to be closely matched to the mesh itself, or else it'll probably clip with the body, and as I have talked about clipping they would never do something like cloth phsyics if it's going to look wrong, clipping is like plague to developers. This means that in a TES game, with dozens of wildly different outfit shapes and styles, a similar amount of rigs will be needed. So while the colliders of the body would be the same, the clothings rig would be specific to each piece, or similar pieces. So a single rig for capes is feasible, as long as 1: all cape meshes are the same or very similar in shape. 2: that none of the outfits they can be worn with will have very differently shaped meshes. < the body will have collision physics for havok behaviour, but I doubt outfits won't contain the information so compatibility between items is probably a rare thing. So I am sceptical of it's implementation.
In theory, any combined rig that would account for a wide variety of outfits would be quite extensive. It's not like the basket ball game I linked to, where everyone is wearing the same outfit. which imo with all the different outfits, and the modular approach to equiping them, will or could get expensive resource wise.