This idea will attract the pvp crowd, however, it will also attract folks that sell at guild stores (whether they be pve or pvp folks). Oh, and in advance, sorry I couldn't come up with an idea for pve'ers ... I'll work on that later.
The idea is 2 part.
Part 1: The first part is to have the holiday drop-boxes have a chance to contain fragments of a new potion ... lets call it an anti-bewitching potion (it would be a gold level potion). Once a player has all fragments in their backpack, they can activate any fragment which will cause the fragments to assemble into a recipe. The recipe gives the user 15 second of immunity to all alchemical poisons, plus standard health, magica & stamina regeneration. These fragments won't be limited to a single holiday event, but will have the chance to drop in all holiday event boxes (so you won't get locked out of the recipe if you don't get all fragments during a single holiday event. You can try for your missing fragments during the next holiday event (or, if money is no object to you, you can always check the guild vendors)).
Part 2: To make the anti-betwitching potion, you will need a specific ingredient ... an ingredient that can only be 'found' in holiday event drop boxes. There are enough holiday events spaced out throughout the year so that each holiday event you can accumulate a small stash of this rare ingredient. Yea, you probably will have to pick and choose when to use this potion, since you probably won't be making them by the thousands, but that is kinda the point. This rare ingredient could either be BOP or not. But, because you can only get this rare ingredient from holiday drop boxes, it incentivizes participation in holiday events you completed the prior year.
Anyway, just an idea. Since ZOS seems to really like their alchemical poisons, it was a way to make the idea of an alchemical poison immunity potion palatable to ZOS.