This suggestion is for Christmas, but could potentially be expanded to cover other holidays if they are widely celebrated enough within the community. I would worry about it getting too excessive if dozens of holidays were considered, however step 1 would likely prevent this being an issue – if a significant number of players didn’t want it to cover a specific holiday then it’d fail its poll and that would be that.
Christmas is the main focus of the suggestion since it is likely the most popular holiday among players, with most of us either going to celebrate it or being from a country where it is widely celebrated. It also has a historical precedent in real life, with an actual World War famously having a day off for Christmas, so it seems fitting to see whether it’d be welcome on a war game.