I hope not, as much fun as Holiday themes can be, they can be extremely limiting. Not appropriate for a Mega Jam anyway.
The Great Pumpkin or Ghosts & Goblins or even worse Holiday Horror games, just too cliché for a Mega Jam.
btw… which version of the engine is going to use?
I like using the most recent version usually but have had problems in the past with using the newest version during a jam but the bug list for 4.9 is very intimidating.