Already started, afaik. :]
I agree with Cerri, .PSD Remix sounds cool. We just need to make the said pack containing stuff to use.
Some ideas for themes: Minerals and rocks and fossils, b/w, 60's, TRIANGLES, books, movies, bone skulls, forest... And under fashion category we could make SOTW based only in stuff like this:
Tattoos, geisha, vintage, glasses, woman/men in uniform, cleavage, water, circus, masked, hair styles, balloons, mirrors, spine, dancing, hats, horses, cigarettes, flowers, butterflies and dears.
I know it could be kind of hard to find stuff for each category but like we did a few times back on ACF, in which people posted stocks so everyone can pick them up to participate in the SOTW. I have a few of each category so I wouldn't mind lending some if we ever do this.
I'll probably come later with some more, but I shove pretty much every idea I was thinking at the moment.
I like Gabe's idea about animals, btw.