Winter Bash is coming soon. Each SE site can choose not to participate. I can't think of any reason why we wouldn't participate, particularly since each user has the option to turn the feature off and the hats will disappear.
I'm planning to tell the powers that be that ELL is "in" unless someone here presents a convincing argument against participating.
To those who may be new to the Stack Exchange: Winter Bash is a season where your avatar pictures may start wearing hats. Some hats are easy to earn, and some take more effort. You can choose which of your hats sits atop your avatar from the ones you have earned. Some use the hats as incentive to do more on SE, by trying to earn as many as they can. (Personally, I just go with the flow and then I watch what happens.)