This is a pretty simple one, but with the addition and rising popularity of RBGs due to BGB, it would make sense to me to add sets for classes like Monk/DK/Shaman (Alliance) etc.
This same thing was done for example in TBC with DK receiving a Brutal Gladiator’s set despite the fact they did not exist in TBC. No need to create entirely new sets. For example, Alliance Shaman could just get the Alliance Hunter’s mail set, possibly with a slightly different color. Same for DK and the plate sets, etc.