My view. Yes, one Showcase will work (and for all intents and purposes is currently working) because there are so few contributors. But you still need some basic organization and simple rules to help facilitate viewers and contributors interest. This will become even more necessary when the number of posters and images goes up. Think about viewers coming to LuLa for first time and not just long time contributors. Why change Landscape as category (or sub-showcase), especially on site called LuLa? It works beautifully. Architecture appears to be about 20 or more percent of images posted, that would be nice too. Why so many threads on bw work? Simply create one sub-showcase for all bw work. You can always post in or create other threads within or outside of BW. These should be at least some sub-showcases under one Showcase. How about the showcasing of Medium format images? Should it have its own sub-showcase instead of a thread? That may drum up interest for medium format. You never know when someone Googles medium format, and what comes up may be LuLa. All the rest can go under One Showcase until change is needed. Very basic. I have nothing against one showcase, but some organization will help facilitate viewers interest. If people want to try one showcase with no categories, by all means try it.
What I like most about contributors on this site is that they often make interesting comments about their images. Stories, why they took an image or what they like about it, how they took it, etc...
JR