Interiors!

Imagine if the devs managed to take space exploration to the next level. Imagine being able to float around in your station through docking ports while having a fairly simple yet modular interior while you explore the cosmos.
Other added functionality that would be amazing would be the addition of life support and some more realistic astronaut functionality - however, the main concept would be interiors for ships. This would also give players a reason to build inspired space colonies and increase game retention as there is more to do.