I'd like to see armor behave more realistically. By that, I mean that heavy armors should have a Concealment penalty, and light armors should have a bonus. Medium armors shouldn't have either. Perhaps this could give rise to a class that was built around sneaking; well crafted for silence, camoflauge (sp), but more expensive and less protective (well, this would only work if the concealment nerf was fixed).
Also, boots should probably be the focus of Concealment armor, and be less protective in general. I don't understand how my boots have more than half as much influence on AC as my chest armor...
An extansion of this is speed; really bulky armor should have a penalty in run speed, melee attack speed, etc, while lighter armors should either give no bonus or a small one. I'm thinking none. If I read it correctly, this is part of the point of having MA suits... it makes much more sense for a MA to use a light kevlar-reinforced suit than a plasteel armor set without penalty.