Mage tower got me thinking about this with heirlooms though it applies to a host of items.
Would you want to see limited time items returned and if so to what capacity?
For myself I would like to see heirloom and removed heroic mounts return as they don't really feel tied to anything meaningful to me beyond showing you were subbed during that time period of the game. While other items like pvp sets I am rather torn on as I can't really see a way to emulate the difficulty of obtaining those rewards during their individual seasons.