Rules: You can choose either a book race, chose to use a custom race, or a rogue faction of a book race (home designs based off of book ships, count as custom races for the purposes of this campaign).
For every player who is in the game, there are 3 "NPC" races that are a mixture of unused book races and custom races from other universe (Imperial Star Wars, Babylon 5, Stargate, etc). And every player and NPC start off with a set number of systems placed on a chart. You can only invade a system next to a system you control, and no player's system will start off touching another player's. Systems grant you resources and research, which allows you to continue building ships and advancing. We'll try to restrict totally removing any players from the game, and we'll keep adding new NPC's as the game goes on.
Book Races: If you choose to play a book race, then you have access to any and all ships under your race's fleet. And because you don't get to design your own ships to make them more deadly, you receive a percent bonus whenever you're facing against a custom race (I'm thinking 10% bonus would be fair). If we could find a way to prevent custom races from using "cheese fleets", we could have no % handicap.
The problem is... things are still stale for this method of playing. So I was thinking that instead of doing research, you can also build and design ships. You can only use weapons and systems present on ships already existing, and you must follow any theme already used by that race (Stealth, fragile systems, no ship has fighters, etc). This would allow you to have fun designing, just like the custom races too. Research for new traits and equipment can be unlocked, provided it fits the flavor of the race (You are not getting cloaking if you are playing Federation ships, for example).
Custom races: If you play a custom race, you're restricted at the beginning of the game. You only have access to 2 traits for weapons (not including accurate, Triple damage and Catastrophic can only be unlocked if you have double damage, Scatter can only be unlocked if you have Diffuse, Telescopic can only be unlocked if you have Focus). You also only have access to 2 different types of Equipment, and 2 different Ship Traits. You're given a set amount of points for a fleet to design your ships. As the campaign progresses, you can unlock research to unlock new traits and equipment. Players are discouraged from heavy cheesing, and custom ships will be reviewed before being allowed (If you have a speed 20 ship with range 3 and Diffuse, Scatter, and Triple Damage on a weapon, get out). Smart designing is good, simply trying to break the game purely for the sake of winning tends to ruin games.