What about composite armor, like in Ultima Online or Siege of Avalon, or maybe Morrowind? I mean that in all of those games you do not wear armor on naked body, in UO you can wear leather/cloth stuff under you armor. In Avalon there even more realistic system, you can wear chain armor under you plate armor.
Also it will be awesome if you add ability to wear robes, cloaks, tunics over you armor. They can add some additional bonuses or just used for social features. For example, if you want to tell everyone that you are member of some guild/fraction you can wear surcoat with heraldic of your fraction, and npc's will react you as a member of whateveryouwant. Also it will help you to recognize allies and enemies.
Also, it is very interesting how you will divide armor items. Will it be "classic five": helmet, gloves, chest, boots and belt. Or it will be more progressive, like morrowind one.
I think that freedom of combinations is much better and interesting than standard sets created by developers.
What you think about this?