I'm quite impressed with the response so far! I'll be totally honest: When I started this thread, it was originally just an excuse to use the phrase "Elemental Christmas".
As I was writing the suggestions for the OP, the Feywild occurred to me, and it actually seemed like an excellent fit! Apparently, a fair number of ENWorlders agree.
There's no correct answer here; every choice puts a different "spin" on Christmas, and not necessarily an exclusive one, at that. (For example, the Plane of Christmas as a layer of the Abyss makes a lot more sense when one considers the chaos and evil involved with trying to find a parking space at the mall on the 23rd of December.)