Hi Dugan:
I like the categories, but I feel that for extra juice, you should categorize it in two more ways: time period and tech level. This would permit you to divide the fluff and rules in several broad categories that would go a long way in racionalization and "universe" creation: Pulp era, steam-punk, 50's, modern, retro-sci-fi, etc.
Why do I say this?... Let me try to explain it with two examples:
First. One of the best systems I ever played with is Starmada. I played briefly Starmada Compendium that a friend brought from UK. At the time we played FT with every miniature we could put our hands into, and usually with BF Gothic minis, though we hated the rules, "guess the range" was so stupid that we usually used it as a joke. I then bought Starmada X and we kept on with our group of players enjoying it. Why? The rules were great. The Adm. Edition was another step up. I loved the new movement rules and the streamining of everything. I have all the books. What do I lack in this rules? The universe. I like the three installments (can I say this in english?) in the three books. Imaginative, complex, open, as the system so well allows it. But I would prefer a unique universe with a on going on history and several very well detailed races, good and bad and a lot of drama. From book to book things would change, the ships would be retroffited, new ships would be added, maybe a new race. Continuity. Under rated. Essencial. It is the growth of the characters, (in this case, races, empires, nations), that we love to see. Luke skywalker could be summarize this way: "A naif peasant raised in a poor agro colony becomes a Jedi Master."
Second. Iron Stars. When I first read the rules (I skipped the storic info and dived into the rules) and I wasn't very thrilled. Than I read the background universe and I started to imagine a lot of potencial. As I was looking for a star combat system for a Victorian Sci-fi Adventure, I come to the point that I decided to move my adventure to Edwardian Age just to stay with this background. So here we have continuity, and the possibility of character (Nations) growth. I think that it is this that sells suplements more than the optional rules (it's the pack, I agree fully, but without fluff continuity, it will be harder) and the ship designs and images, of course!
So I think that a very well conceived and open universe in this Kaijun project is a must.
Sorry for the long explanation. A teacher has the bad habit of going on rumbling about endlessly...