As far as difficulty goes, I could write the code in 5 minutes that would make all the layout colors and images easily switchable by Zeality or according to the date, with the upper right hand image completely random.
Here's what's customizeable via CSS:
The horizontal repeating background of the logo (the orange bar part).
The left image of the logo (the logo itself).
The background of the page (Crono and the gang).
The page's colors.
The image on the right can also be customized by adding a script that outputs a random or selected image. However, I'm shooting for quality, not quantity, so gathering lots of low quality images to randomly place there isn't our goal. Every random image should blend seamlessly with the layout it's designed for. It shouldn't draw any attention away from the content or the navigation links.
If people are interested, then I'll provide some general tips and we'll set up a thread to allow users to show off their designs, featuring the best ones on the site.
Also, for branding purposes, I'd like to keep the logo design the same, no matter what. The current logo design is lightweight and simple, though I might experiment with some other designs before finalizing it. Once final, I'll be making a variety of downloadable image files available to allow others to use it in their sigs, banners, and images.
Now then, here's what I won't do: User selectable skins. We tried this a year ago, and it required a lot of ugly code hacks to get all the different parts of the site to work together. Why the difficulty? There's three different template/skin systems used by the Forums, Encyclopedia, and News/Story scripts, and they all have different authentication and session management systems. Tying them together is at least a full day's work, and I don't have the time to waste on useless things like that.
So yeah, continue with the discussion.