Something I would like to get away from is 'armour sets'. In most MMOs you have various 'sets' of armours that give bonuses if you wear all of the pieces. This invariably leads to all Rangers of a given level range looking the same, all Bards of a given level all looking the same etc. Raids begin to look like sets of clones of just 5 or 6 people 1 set per class).
So how about this:
1. Armour of the same sub-type get synergy bonus: (eg all half-plate, or all full-interlocking-plate etc) but only for determining movement penalties for wearing them. This is to reflect that fact thtat these types of armour were designed to be fitted snugly to the others of the same type. this matters less for cleather and almost not at all for cloth!
2. Each piece has a bonus for material type, crafted quality and then enchantement etc.
'Finley's Armour' style: He favoured lightweight armour (lower AGI penalty, +Bonus to STA, lower +Bonus to AC)
'Merrick's Armour' style: He favoured heavy solid armour (big +bonus to AC, +heavier weight, bigger AGI penalty, -Penalty to STA)
Now players just wear whichever bits they like (or find/make) and mix'n'match to their hearts content.
MTs might favour pieces of Merrick-type styles as they offer more AC, but at a cost to STA and mobility. Rogues may favour only a single piece of the heavier style and the rest of a Finley-type style to ensure they do not run out of STA mid-combat.
There is no reason why there cannot be many many styles/types of armour .... and no reason why 'master' crafters cannot choose the types of bonus they focus on for their pieces of armour - not to mention giveing them perhaps freedom to use 'templates' to determine the armour piece's *look* as well as stats.
This wopuld mean that unless you commission a crafter to make you a complete set of armour in one (matching) style and had them all made/dyed etc the same, you wold be very unlikely to see people in anything other than mix'n'match armour. A full set of matching armour pieces would be the exception, not the rule. Even then, they would likely comission different styles from each other, and certainly different colours or inlays.
PS But STILL pls pls pls ban any pauldrons large enough to use to sneak a halfling into town with!