Village_Monk, I just tried the Halloween theme. It's cool!

Specially all the corn. LOL! Looks nicer than the original turnips/carrots, actually.
Anyway... I haven't tried the Thanksgiving mod - will install it in November.
You said you were gonna try to do Christmas ones. I had a couple of ideas... mistletoes on the trees... holly berries on the berry bush... and maybe, if you can, change the garden from the current batch of flowers to wintry flowers and bushes.
Electricity isn't available on Isola, so X-mas lights wouldn't exactly be appropriate, but you could string up decorations on the huts. Maybe green and red colored balls where the little lights would usually be? Sort of a ornament-based popcorn string concept?
maybe have this cute little pine sapling on the research table (mini christmas tree)...
Oh, and outfits. I think at Christmas, there should be a red and green version. Dunno what the idol could be turned into.. A giant reindeer?

That's about all I can think of right now.