Just an Idea. Fuse it whit the set idea mybe? How about add 1-2 shop's in town when/if player clicks on it, it will only show there class items/sets/upgrade/quest/etc...
Classes should be by "Tier of ....." Right now the classes of Tier's arent totaly balanced i think
For shops as tank collect from difrent areas all armor based items ex: Armor of Existance; Hell Armor; Void Armor etc... and mybe add some extra rare item lot of options
combine it in set at shop then make a nother 3 difrent set for the 3 do combine whit some new boss item for 1 complete set mybe even add + upgrade
like ya need ex: +5 Armor +5 Shield +5Helm +new boss do combine it
Becose i think there will be a 3th world stronger then Chaos so ya need Good items, This upgrade should be hard egnuf :S