I too have a map that I didn't finish in time. I'll probably need another month now because I stopped work after the first release and now I'll have less spare time. Here's a couple of screenshots in which neither fire or brimstone are greatly in evidence:
http://i.imgur.com/liU6nAB.jpg
http://i.imgur.com/xq5HQVY.jpg
At the moment I'm thinking that I will release it on its own, unless someone sets up a DLC deadline that is realistic. It's not like the Quake release schedule is so crowded that no-one will notice if you make a post to announce your lone new map (I hope).
I agree with Daya that it would be good to release as part of a package, but I agree with WarrenM more that if every jam project is going to have DLC now the original deadlines will be meaningless.