The whole 'living on gas giants' is debatable, as yes, logic says hey live in moons, yet when you check those worlds you get cloud cities on the atmosphere as a picture, and a surface area that's insanely big (Which I take as making new floating cities until you fill the planet), I once had the Skylaxians in a gas giant, and by late game they were expanding habitable area so fast their population just kept on increasing and stabilized at like... 5 trillion or something.