I don't see why wildly different concepts can't be worked into the same mod, even if they are polar opposites. You could set them up as different paradigms similar to that Exodus mod Pax was working on before he vanished.
A wiki as it is works great for collaboration on ideas and concepts. Its just the actual implemented entries in the data files that will be trickier, especially if you want the entire data files viewable. If you give me some time, I could work something up out of the codebase of
http://adamant.spaceempires.net/database/ that would allow people to submit new items and modify existing ones, keeping track of all of the older versions of each item in case something needs to be rolled back. This could definitely be dumped to text files on demand.
Combine this with a wiki for discussions... hrm.