Hmm, I could certainly see that being interesting~ I even like the name of "The Challenge." xD
Really, the only issue I see with that would be just regulation (for fairness, checking for original work, etc.) and how on earth they would be judged against one another.
For example, the map makers could certainly add many, many more dimensions to their creation than an object maker, or even preset maker, because they're essentially using objects and the like simply to create their theme. So, it might be a bit difficult to judge.
Perhaps they could add a different dimension to the competition, by incorporating a "Favorite Map", "Favorite Preset", and "Favorite Object" along with the all-out winner of "The Challenge." That might be an idea.
I do see where you're coming from, though, and I do like the idea~ Thanks for the input. :3
Side note*
I'm not sure, but I do believe that a year or two ago, they actually did have map making competitions... Unfortunately, though, I wasn't nearly as active on the forum, so don't hold me to that. I can't be sure. xD