There is a vast amount of different player created content, from missions and mission editors, handbooks and key-binding reference documents, mods and extensions, and even uniform designs. Combining them in to one large section could get confusing. Also, there are already places for other player created content, such as the Mission Scripting section, which contains player created mission scripts and details about the player created the mission editor.
I am in full support of a section just for mods however, collecting those such as BSG and Star Trek mods in to one place. There seems to be no obvious place for details on mods to go at the moment; Off Topic is defined to be more general and suggests that things not directly related to how the Artemis game works or is played should go there (e.g. uniform designs). I can see why mods can fit into this category, but with so many I can see the justification of expanding the forums.