They could use a redesign. It has hardly changed since the early days. I looked at results for the current challenges and it looks like activity has dropped off quite a bit. It seemed like there used to be hundreds of submissions for individual challenges, but now the highest one is like 50.
The idea I was trying to convey when I mentioned it is that if you don't have a rigid set of topics, you can be more inclusive of different types of photography. The downside is that compared to set days, planning becomes a bit more complicated.
The latest list does seem to hit most of the general topics, though.