Uh, not to be a downer or anything. But isn't the point of FreeStyle to be, free?
Ya know, no rules, no regulations; to do whatever you want and be judged purely on creative effort instead of strict and rigid scales of concise protocols to achieve a certain artistic point?
TL;DR - Isn't it the point of FreeStyle to be judged strictly on creative effort instead of trying to achieve a theme?
What I'm saying is you don't really need an idea for FreeStyle, just host the contest, give everyone a deadline, and let the people go bananas.