The Season of Giving
Each Winter Veil, the mail boxes of Azeroth will have an additional feature.
This feature allows you to place one or more items (or gold) of your choosing in a nicely wrapped parcel, and send it to a random recipient.
There would be some sort of bonus depending on how much you give - something fun and relatively useful to really incite people to share what they don't need.
Everyone who's subscribed during the Winter Veil will be in the 'lottery' and may receive gifts from the anonymous Santas of Azeroth.