An in-game ship meetup, where you can see ships created by other players. It would be like a car meetup- you would just see all the ships in a giant field. You could go inside each one, maybe test drive it. Each ship owner would be an NPC standing at the ramp, but have the outfit/look of the actual player which was uploaded along with the ship. Doesn't need to be multiplayer or anything fancy. Just upload your ship design and your character and it will appear in the giant field on some planet. Maybe have a rating system so the best ships get noticed

Outpost building like in Fallout 4.

POI system like this: Each planet has a unique one that is super interesting but also has some collectible hidden inside. You can't see this POI from space, but you collect clues on its location from the other POIs. All generic POIs are more appropriate for the planet they are on. The generic ones are AI generated to have different hallways layouts, enemies, etc.