Gas giants are, like name implies, a gaseous planets. It isn't really a good idea to try to land on it, when we know already that plunging into Jupiter, Saturn, Uran or Neptune will be end of you due to pressure, and unless we make major improvements in both survivalibity, everything sent down there is on suicide mission.
In StarSector however, it's a bit different. Currently, when creating a colony on a gas giant, colony is just... kind of there. I know we're not striving for biggest realism, but I think it would be good to think about other options. How about orbital stations?
Instead of creating colonies, if player wishes to estabilish a colony on a gas giant, he'd be forced to build an orbital habitat. It could take some time, be expensive, but increase accessibility greatly, and have rather small population, which limits it to only single industry (mining). To increase that, player would need to enlarge the station, which would in turn be rather expensive, etc, etc.
I could think of specific mechanics of that, assuming it's even possible in the game.
Thanks for your attention.