Hey Riyu. As I recall, we were nearly the only people who took much interest in switching to a non-default favicon. And as it happens, we both now have the ability to make the switch. So I was thinking sometime in the near future we could show off a few possibilities in another blog post or something. Worst case scenario: still not many people care, but then at least we could pick one.
It does seem Wikia is a bit more limited in this regard than it needs to be, so it has to be a 16x16 image, no greater.
I don't know what level your image editing/creating skills are at, but there's nothing very special about making an icon. The most advanced thing would be setting the background color to transparent, unless you're going for a full square image. From there, there are various sites online that will let you feed it your image file and return it as an .ico.
One of my two is pretty much the old H!P logo with a different color scheme, though that's flexible. If you want to pick a leader picture (or a few), I can try to resize/crop it as decently as possible.