It's possible they developed some sort of chemical or heat smelting techniques that worked under water. They may have also been clever enough to figure out that you need oxygen and other things in gas form, so instead of water tanks, they built air tanks designed to create a non liquid production ...

An intercept mechanic would be really interesting. As far as I can find, it hasn’t already been brought up or suggested.
The ability to intercept ships in travel and engage. A player could intercept an enemy fleet before it reaches a planet and engage in combat. This would give the sense that a ...