I don't really have time to participate in any challenges but thought you all might like this.
https://www.udk.com/showcase-amazing-one-texture
It shows what a developer did with only one 256x512 texture. Could make for an interesting challenge. Create a scene and use only one texture of a certain specified size.
Don't be satisfied with what you can do but rather strive to do the things you can't do!
Exceed Expectations!