I totally agree with removing the Mage Armor property, but as far as making everything medable, I Totally Disagree.
In fact, I think they should take it the opposite direction. Cloth, leather and leaf ONLY for casters (that includes making cloth armor pieces for humans and elves like they did for Gargoyles). Metal armor for combat oriented skills. I also think that Swamp Dragon armor should only apply if the rider is also wearing plate armor. Wood armor should be wearable by both humans and elves, but only medable for elves. Humans should be able to med, but with a slightly lowered success rate, in studded armor.
If you think about it, it makes more sense in realistic terms, if one can apply the term "realistic" to anything UO. Take a look at stealthing. The devs went out of thier way to make the whole process seem realistic--you load up on clinking, clanking platemail, you fail at stealthing. If you walk around in supple leather, no problemo. I hear that if you lube up real good and get naked, you never fail at stealth (that's what oil flasks are really for!)!
OK, I jest, but the gist of what I am saying is that no mage was intended to go clanking around in platemail. The closest we got to that in the Ultima series was Blackthorn and Paladins, and for that there are necromancy (with it's various mana-regen schemes that do not require medable armor) and focus.
Granted, there are some seemingly useless armor types, but the above would remedy that provided they included properties on cloth so that cloth wearers had some control when crafting. This would require the introduction of something along the lines of colored ingots, leather and wood but could be implemented by different cloth types instead--wool cloth, cotton cloth, abyssal cloth, etc., so as not to interfere with all of the BOD cloth colors and such that would still be used for non-armor clothes slots. As is, the use of most of the colored resources is pointless--you simply go with what has the highest properties. I think this can be fixed by re-balancing the properties on colored resources--one end of the spectrum, say dull copper, is good for casting, ie. more likely to include elemental resists and properties that benefit a caster. The other end of the spectrum, valorite, would include higher physical resist and be more likely to have combat related properties applied. This could actually be applied to both colored resources and runic kits--they would be equally valuable, but towards different ends--one type is better for casters, one type is better for combat types, everything in the middle is varied blends of the two.
You might see a pure mage in cloth armor, a dexxer in studded and a pure tank in plate...as it used to be in UO. To be honest, I still don't understand why they strayed from that formula in the first place.
I'm sure I've just ruffled some feathers...but hey, my two cents.
"Metal armor would actually become useful again."
It is....just not for mages.
Edit: I forgot Bone Armor. While they could actually implement types of bone (ie Daemon bone, Dragon bone), I don't think it necessary. It can be made more useful by giving the pieces some automatically applied properties (in various values) during crafting that benefit users of Necromancy and Spirit Speak. Perhaps a slight mana boost when Spirit Speaking on a corpse.