In writing StarCluster 3, I have rolled almost everything that was a supplement in SC 2 into the main book - Robots, Aliens, Created Creatures, Vehicle Design, Spaceship Design, Weapon Design, Religion, Biotech, and more. So some of the playtesters who were familiar with SC 2 have asked me what I was planning on making available as support.
Thing is, I'm going through a big change in attitude with regard to supplements. I want to make SC 3 completely capable of standing alone, with only the core rulebook necessary. Towards the end of SC 2's effective lifetime, the core book alone would *not* give you the full StarCluster experience. When I recruited a new player for an online game, I sometimes sent half a dozen different gamebooks just so they could create a character will all options "on". That was a pain in the butt for me, let alone someone who wasn't the designer! The rules were scattered over a ton of optional materials, and it was hard to remember just where the relevant stuff was. I'm really happy with this aspect of SC 3 - you really do have everything you need.
So, supplements you need are out. Supplements you might want are in. Timesavers, or kickstarts to your imagination.
One fertile area would be pre-made sectors. Sets of connected star systems, areas you could adventure in. They would be set up so that you could connect them together as required, or use one as a base and expand it yourself, or tack one onto a self-created Cluster.
Systems and Worlds might also be available. Things like Glorianna and Chariot, which you could place anywhere in your own sectors.
Sets of pre-created ships, vehicles, and/or weapons would be cool too. Specialty items for specific purposes.
Expansions would also be cool, so long as they expand and not re-create. A Psionics book that gave some rare PSI skills, along with professions to obtain them. Books on Backwards (Tech Level 5-7) or Primitive (Tech Level 0-4) worlds with education, professions, equipment, and cultural overviews would rock, and are most probable to be forthcoming from us.
That leaves what you all will come up with.
What will be different is that I'm opening up the system and setting for development by others. Not only am I perfectly OK with non-commercial development, I'll be putting a commerical RPG development package containing SC 3 and a license to create and sell anything you like for SC 3 up for purchase, for $1 more than the standard DL. So, if I sell SC 3 in pdf for $12, as is very likely, for $13, you can get the SC 3 pdf and the license, with an official logo you can put on your product. All you have to do is register it after purchase. The only reason you need to register it is some people hide their names in pdf shopping, and without registering, I can't verify if you have a license or not.
How's that sound?