Hey, this is a neat little idea. I most likely won't participate, I'm not exactly the best mapmaker, but I do have some suggestions:
First off, I think TC KotH is a very solid choice. My reasoning behind this is that the map should be big so that the effort that everybody puts in pays off anymore. Say I want to detail, being bad with layouts and all. Problem is, the map is tiny. 2fort size. So, most of it is already detailed. Lame. So the map needs to be big, right? So that means A/D push maps... or, TC. But TC is not particularly good, at least, Hydro isn't. This seems due to the very nature of the gametype, it's like push-CP but bad. But KotH eliminates all the problems that actual TC has, and after all, it is Territorial Control. King of the Hill fits quite a bit thematically.
Anyhow, I have a suggestion for how development of the map goes. Unless I'm not much mistaken, TC maps have 6 territories. So, I do think that while allowing everybody to contribute is a great idea, I think that we should at least have people who are known for being good with layouts to come up with the base layouts, since we would want the map to be fun and successful. We're talking people like... hum, Icarus, Eerieone, Youme and the like. Split it off into 6 different lots and give 1 lot to each prominent mapmaker, and let them do the layouts for each zone. That will mean that each zone will be very distinctive in its own right, and they'll most certainly be good. That being said, I would say very little to no detailwork should be done by them. Why?
Well, the rest of the community contributers need something to do, don't they?
Just my two cents, anyways.