I have tons of ideas, but those feel like cheap ones:
* Remove "cramped space" from negative morale modifiers. Not everyone is claustrophobic (but that'd make neat character trait!)
* Add "In my room" as positive morale modifier. Man's home is man's castle
* Less negative effects from mining. Right now, digging a long cave feels like most dangerous task ever
* Remove "trading ship in orbit" from alerts, or better yet, make two-tier alert system where such low-priority alerts appear in different-colored icon or simply as message on upper right
* Extremely cool would be to actually see shadow of trading ship slowly going over game map. Since it's far away, it would be quite large and impressive. It could even disrupt solar panels (although occurrence of ships should be much rarer, otherwise it'd just be annoying)
* Stackable food or single-tile container to store stacks of prepared food. Also known as fridge
* Some scheduling system for designated cook(s). Like "make colonist+prisoner amount of food twice a day" Right now you either micromanage food all the time or make tons (infinite) and lose a colonist to this never-ending task, not very conservative approach to ingredients neither, since stuff rots over time
* Handheld lights. Nobody really goes to dig endless mine with no flash- or headlight
* Better solar panels. They feel very unbalanced right now. So far in future, solar power efficiency should be much higher
* Prisoner escape attempts
* in a game where you colonize unknown world, there should definitely be injury and disease system. And various diseases, born immunities to them, viral outbreaks, isolating patients, broken feet and hands (and how they affect colonists work), etc etc. This is not cheap to make, but groundwork for something like this is easy enough and could be handled with character trait system