With the new Custom Contract System that Kane has begun to bring into the game, there are many possibilities that it opens up in the way of adding small amounts of content for the game.
Most major Holidays could have a Contract Vendor added, and yes I understand this would add to Kane's 1001 items he is working on, lol.
The contracts could be for the content added for each Event, such as kill a number of such and such creatures or combination of creatures (kill 10 x, kill 10 y, and kill 10 z) or to kill a specific boss (if there is one) or a combination of bosses.
Rewards could be the normal rewards, special holiday themed items, or rewards unique to the Contract For the specific Holiday Event.