This may be something that is already being planned, as I know a lot of the artwork shows some heavily armored vamps, but I would really like to see different armor types at each tier. I think that just three categories could be enough, with Heavy, Light, and Robes.
Heavy Armor would be plate armor (alternatively, depending on tier: chitin, bone, etc.) that possibly trades in some speed for extra health, but has set bonuses that include some limited damage reduction, life steal, and/or Physical Power, and any other benefits that lend to the frontline fighter fantasy.
Light Armor is the tier we have in the game, with bonuses to movement speed, attack speed, crit chance, and Physical Power, and any other benefits that lend to the rogue and skirmisher archetype.
Robes might trade in some health for Spell Power, with set bonuses that reduce the cooldown on spellcasting, increase spell crit chance, and anything else that lends itself to a mage archetype.