I would go with Frosty and Rudolph and the Grinch. Islands needs more kid friendly stuff. Suess is beautiful but the rides are really lacking. But I do agree that anything Christmas related would be best indoors and climate controlled, minus the Grinch coaster.
Well they could do a Knockturn Island sort of thing where the entire thing is indoors with wait for it snow falling....snow on the ground where you can build snowmen. Hot Chocolate smells, String lights. Just pure holiday magic.