The one thing that I always considered unrealistic in KSP is the need to place some things on the outside of the ship. We should be able to put stuff like computers(mechjeb,kOS,kerbal engineer),batteries and other utilities on the inside of a command pod. A system like that could base on the concept of available volume in the capsule and each items would take some of it up. Just a small idea that I decided to share with you all.