hope to see it ingame :-)
That's actually not a bad idea - we could use an "easter egg" or two in the game. Heck, look at VLC media player - the last few days it has a custom icon when running.
If you really wanted to go overboard, not a serious suggestion, but just an idea - perhaps around the 24th-25th of Dec in each in-game year a sled pulled by reindeer could appear on the geoscape, flying high.
Of course then there would be the question of what it would do if it came near a UFO. (Does Santa pack an anti-alien plasma rifle, for the obnoxiously bad people on his list? I forget exactly how the song and story goes...)
More seriously, that type of stuff would make an interesting mod for the game.