The problem withe the assumption fromt he OP is that all Glass armour will have to look the same. They could introduce multiple styles of glass amour while still having it be distinguishable as glass amour. Just as WoW has a great deal of plate, chain, leather or cloth.
If the concern is with the stats of the items then I have little to no doubt you will have some form of attribute system in TESO either in place on the items (likely) or through enchantments (to either augment additional attributes or to stand alone).
The largest problem as has been mentioned is that whilst WoW has an enourmous amount of armour very few are actually useful at any given time if the player is playing in the current expansion, which leads to most armour being little more than appearance fodder or vendor fodder. I would like to see varying styles visually so people can find a look they like (and visual customisation is important in MMOs for a great many), while having meaningful equipment rather than weekly gear changes because item A has 5% better stats.