Ion's mention of adding evergreen content really stuck with me -
Holidays are a very good example and also the battleground flavors like raid battlegrounds and "Eye of the Horn" etc.
What is some good content you personally would add to the game to make it feel like a living breathing world?
I was thinking about palyer written-stories which you could buy at the auction house - or custom transmogrification armor sets which you could buy from other players - or player housing....
What would you add?