Well, I most definitely hope that we will have more slots this time. Definitely more then Oblivion and hopefully more then Morrowind. To add to Morrowind's list, I would add cloaks (we need those!), separate glvoes/gauntlets, more rings, I think 8 would be a good number, belt and then ear rings and for the beast races some items that can be put on tails - like special tail armour or tail jewelery. This could ballace out the fact that the beast races cannot wear certain armours (as in Morrowind). The fact that you can wear clothes under armour (and that the clothigs shows under certain armours) goes without saying.
But the true potential of layered clothins adn armour would come if the clothing actually ment something. In TES your clothes have no impact whatsoever. You can wear the prisoner's clothes of the Arch-mage's robe and there is no differece. People around do not care. Why to put your armour under a robe if noone cares whether you are armoured or not?
And definitely separate skirts and pants. I want my male samurai to wear a skirt and my female rogue would far more appreciate pants.
As far as ballancing magic items goes, In Morrowind this was not so much a problem. If I remember right, only quest itmes you had to find (and even not all of them) had a constant enchantment effect and to create your own, you had to kill a pretty strong enemies. So even if you could have 10 rings, most of them would only be "cast when used" items, which is not that much overpowering.
Unfortuantely I fear that Beth will continue the course set by Oblivion. If it is not tied with more advanced sword bashing and if it does not push the graphics to a new level, it is not important. And such minor and inferior things as role playing (which also contains the customization of your character to your liking be it his appearance or his attire) are being mostly pushed aside. It is pretty obvious even in the fact that it is ecpected in Oblivion that you will use armour no metter what. That is why all clothing is uselss, robes are (for some very few exceptions) totally uselss and it is obvious that the devs paid very little attention to them (in vanilla game being only four robe meshes, one of them being unique, another semi-unique and one specific and only one ONE!!!! with a female version).
The reason Morrowind had more diversity was because of its graphics. Devs could get away with the diversity because most of the armors lacked any 3D-definition. Sure, there were bumps and such on armors to signify that some pieces weren't just blocks, but the time it would take to individually sculpt pieces of armor to great detail would be tedious. What Bethesda did with Oblivion was make things more efficient. Why wear pants underneath chainmail greaves? you wouldn't even see them. As for pauldrons, most are generally attached to the armor in the first place. There are some pauldrons that don't require the chest piece, but allowing pauldrons to be seperate, just for the sake of a few exceptions, would be annoying.
Well, in Morrowind, there were many armour pieces that did show the clothing underneath. In Oblivion your cuirass covers you from nect to waist and to wrists. In Morrowind it only went to the shoulders instead of wrists, so if your pauldros did not have elbow caps you could see your clothes there, same goes for greaves.
The pauldrons are generally attached to cuirass, yes, but why do they have to attached to a cuirass made from the same material? Why I cannot attach steel pauldron to iron cuirass? And what the pauldrons look like is not decided yet. For all we know, they may all look the way they could be used without cuirass.
And as far as tediousness of the job goes, I have to points to make. Firstly, this is an important part of the game, or so it seems as these threads do appear every now and then, and if it is important, then the devs should spent a lot of time on it. And secondly, making a model is one thing. separating it so several parts (i.e. dividing pauldrons from cuirasses, ets.) is not so difficult. Sure the devs would have to "pre-make" the slots, but that does not effect the individual armour pieces much. As the armours are in Oblivion, it would be very easy (and I have seen about all of the armours in the 3D editing programmes)to separaet them in a Morrowind fashion if the number of slots would be made higher.