I can see one major and very important argument against this–manpower.
Deeplow is the only active mod I’ve seen here, and Sven will help out with the Tangents subcategory (my temporary name for it). That makes two volunteers with many other things to do in their lives.
Opening up such a category without increasing the threshold for entry would mean opening up the floodgates. For example, if the Tangents subcategory suddenly became popular, which is not out of the question, then there’d be droves of people from across the web who might not have interest in Qubes clogging up the moderation queue, and that opens the forum up to a lot of abuse and issues. Getting new mods aboard is troublesome; getting new mods aboard in short order is worse IMO–best to have trusted people modding.
On the other hand that might, as a side effect, drive up interest in and adoption of Qubes, which might be a positive development to some, but I think the risks outweigh the potential benefits.
I’m in favor of having a forum for topics tangential to Qubes, but I’m not in favor of unrestricted access since that might lead to disastrous results for the overall forum–those who participate must have, in a non-trivial way, demonstrated an interest in Qubes and positive contribution to discussions, otherwise why be here in the Qubes forum? Why not go to one of the myriad other forums?