I have three ideas for contests, both of which are fairly dumb ideas, but would be interesting.
1. A 24 hour mapping contest. This would be completely a joke, and could work as a joke contest. Not much to be said about it, make a map in 24 hours.
2. Artpass 2. An artpass contest, or just a detailing contest, where one map is detailed by several people at once. It would be interesting to see what people could do and accomplish if everyone is trying to turn the same developer texture theme-less map into what they view the map as.
3. A junior mappers contest, or a novice mapping contest. This could help bring in new mappers to the community, and help newer and less experienced mappers improve their skills in a fun and rewarding way. This would be a contest where only less experienced or newer mappers who have never won a contest could join. A contest like this would last somewhere between 2 weeks and a month, and would require mappers to come up with unique and interesting ideas to hone their skills and claim victory in a contest with mappers around their own ability. While this is contest is running, a professional or experienced mappers contest could also run. This would be something similar, but only experienced and award winning mappers could enter. A contest between professional mappers would push limits and result in some very interesting, entertaining, and professional maps to be created for the Team Fortress 2 community.