Please pardon me if it's a stupid question, as I haven't really done a lot of work with categories in the past. But does that sort of change really need a CfD? I think that if I had found myself with a similar sub-cat idea, I would have just gone ahead and done it or, more likely, thrown it at a relevant project talk page to see if there were objections. Of course, maybe you weren't able to get consensus at the project, hence the post to CfD. Again, sorry if this seems stupid — as I branch out into new and different tasks, I just like to understand the thinking of people who are engaged with them more regularly. I find it helps me with my own decision-making.