There is a lot of unused armor artwork that has existed for several tier and season sets. Let me show you a few examples.
Death Knight - Tier 11
Notice that a green version exists. Yet this set has never been used.
Let us look at another example.
Warlock - Tier 11
There are two alternative versions that have not seen use in-game.
Wouldn't it make sense for Blizzard to incorporate these set designs in the game in some way? Perhaps in the form of cosmetic armor that may be purchased with either gold or justice/honor points, depending on where the set originated from. Providing multiple payment options would be vital, as it can act as either a gold sink or as an investment of time.
But let's not restrict this to unused armor designs. There are some designs that have been present throughout WoW, particularly NPCs, that would make for suitable player-acquirable sets.
Example - Baron Rivendare
Refitting his armor and making it available for death knights seeking to look more akin to the older generation would not require very much effort, yet provide another area to dump gold and/or time in for players.
There are other examples throughout WoW that may be listed, provided that they make sense for a certain class.
Overall, what do you guys think of this idea?