It would be awesome to have a challenge mode for the old dungeons. It could work something like for every expansion you finish in gold time up until Cata you get 2 parts of a set making a total of 8 parts. And these sets could be new HD versions of old iconic sets such as Paladin T2, Rogue T2, Warrior T6.
Just an idea but that would give players a lot of content to be entrained since there are so many dungeons to do.