I've been playing the game for a while now and I enjoy it a lot, however the single player it's very random. You can get a great start and manage to construct a ship with only one or two factions launching attacks on you however I've played games where I've been attacked by five factions at a time which makes the game impossible. I believe some sort of diplomacy system is in order, maybe your at war with a random neighboring faction to begin with and the rest your at peace with. Maybe different factions could have attitudes like aggressive,expansionist, unreliable, peaceful or defensive. This will allow you to make alliances with other factions however inevitably have to war with the aggressive ones.
Adding more depth to diplomacy you could implement trade between factions. For example you could make suspendium,gunpowder, coal, wood, iron, clay(for bricks) and stone strategic resources. Certain cities might be abundant in some resources but lack others promoting conquest and/or trade. Factions could exchange resources or just sell them to each other. This would also prevent big factions from snowballing because an empire might completely lack a good supply of iron preventing them from getting enough high quality armor they need for their ships forcing them to use poor materials, like wood or bricks, leaving them vulnerable. Adding these strategic resources to the game would add lots more depth to game play as players would build their ships based on other factions weaknesses.
I'm sure being an indie developer is difficult and I don't want to topple "the plan" but maybe in a soonish update your could implement the foundation for a diplomacy system so I don't get Zerg rushed by ten factions.
Written by an Australian nerd who clearly has nothing better to do at 1:30 in the morning :)