OK, throwing out an idea here...
In my latest game, I took a good gander at the 0.80 Warrior tree, and saw Plate buried towards the back of a tree of around 4-5 picks as I remember. Meanwhile my heroes are packing around all of this plate/chain stuff they can't use until much later in the game, assuming they earn enough levels. This seems silly on some level, especially for items that aren't boosting my defense at all/very little (rusted chain as an example)
Anyways, on to my idea...
In the 'olden days', I used to be a huge fan of Rolemaster, a RPG system not so affectionally known to some as 'Chartmaster'. In that game, all armor had encumberance penalites, and skills that could be taken to offset those penalties. There was still a 'minimum penalty' as well as the base/maximum penalty, but as characters allocated skill levels to armor, they became more maneuverable.
Armor skills were 'similar' to each other, so if you bought skill in one armor, you earned lesser ranks in the other armors...
Also, armor interfered with spellcasting. 'Cleric/Channeling' had huge penalties for metal armors. 'Mage/Essence' magic took penalties for ANY armors tougher than cloth/robes.
SOOOO, rather than saying in Elemental 'yeah, here's this Rusted Chain, yeah we know you could just pull it over your head and wear it, but your hero is too stupid to know this', you assign a larger base penalties to armors, and instead of having 'Chain/Plate Skill', you have a skill that significantly lowers the penalty for armor.
I don't think you need to break this between armor types so much (too clunky), but simply gain a greater bonus to offset armor penalties as you choose more levels on that tree. Sooo, say chain starts with a -5 penalty, but each level will reduce this by -2, to a minimum penalty of -1. Plate might start at -8 or worse, with a minimum penalty of -3 or somesuch. Essentially, to recap, each skill level would reduce the penalty by -2, to a minimum amount that is at least -1 or more (depending on armor type).
Also, to 'discourage' spellcasters from wearing heavy armors, the mana cost for spells could be increased, based on the heaviness of the armor. So casting in Plate might TRIPLE the cost of a spell, Chain would Double mana costs, and Leathers might increase mana costs by 25% or somesuch. In tactical combat, of course. Casters can always take their armor off for a few seconds to cast that strategic spell.
This also makes crystal armors and such more interesting, as they would have a lesser mana penalty for casting than say regular plate.
This incidentally gives Mages Robes more importance, with more interesting options such as a Mage robe that grants 'chain-like' protection, adding to the flavor of the items.
If encumberance rules are brought back, I think that's the better way to go. With tweaks as appropriate of course!
Those are my thoughts on another approach to encumberance and armor penalties, and another way to balance spellcasting versus weapons and armor.