First, are you saying WoWwiki isn't going to be just about World of Warcraft anymore?
Wow... I loved using your guides for a couple things.
And to answer your question, Categories are already their own namespace. We are in the
process of writing an extension that will let you pass a namespace as an argument to a
Category page so that you only see that Namespace worth of that category. Something like
Category:Dungeons/WOW which would mimic the Special:PageName/$par functionality.
We haven't even started anything except thinking how nice it would be, so please feel
free to write it and post it!