We started 4E many years ago.. 2004 or 2005 I think. We had several successful years of it before it tapered off a bit. The themes also evolved. See https://en.wikipedia.org/wiki/GameDev.net#4_Elements_contest.
The original theme was the 4 elements of fire, water, earth, wind. All four elements had to be incorporated somehow. Lots of creative entries. The second year was the biggest ever with over 50 entries and some amazing games, a few of which went commercial after the contest. Over the years we learned how to handle judging better and generally how to run contests of that scope (6 month development time). The themes also evolved. I remember one theme involving ninjas and pirates, for instance..
Contests are something GameDev.net will be doing again as they offer a lot of value to the community. We'll possibly have a bigger one later this year - which is why I'm proposing something like this contest could be an officially sanctioned/sponsored contest with promotional power and organization beyond the GDNet Lounge. Based on the polling so far it looks like everyone is interested but nobody really wants to organize it and there are concerns about judging - these are things we can handle more directly with an official contest.
I also think it's fine with this being a community-driven contest, but the officially sanctioned option is there.