But... if we make a theme for each season when will we ever have a
classic MLK theme?? We need some consistency, people. The only reason Google changes its logo a handful of times a year is because they want to keep the design regular throughout the year.
And this goes back to my previous reason for why this probably won't be a good idea. As I said before, Moka would need to update the new themes each time a newer version of phpbb came out, which would be a pain in the rear-end. Some text would be hard to read, and the colors wouldn't match well with the rest of the MLK domain.
I'm not saying we shouldn't have any new themes at all (heck, I would actually enjoy a change of design in MLK) but I'm just saying that we can't have one for every little event. ^^
Of course, if Moka decides to go along with your ideas anyway, I'll shut my mouth and pretend I never said anything against this lol.
EDIT: A Halloween theme would be epic.
So would a New Years theme, a Valentines Day theme, a Christmas theme, an Easter theme, and maybe a Thanksgiving theme (again not sure since this is an American holiday). Oh, and maybe a TLK theme for TLK's Sweet Sixteen?