As someone who never participates in artistic contests (cause whenever I open photoshop and try to make something freehand it turn to be a catastrophe) but always follows their flow, I would like to see and UI contest. But it is, as said above, a big job and shouldn't be started unless there is time and people interested to participate.
Taking a custom model and reskining it sound always cool. It would be interesting to see how others would recreate it.