I have been working lately on the defense missions (both the designed and procedurally generated variety). These missions are not ready yet and will not be in the preview. The basic idea behind this kind of missions is to launch from your base and defend it against several waves of attackers. The difficulty in designing these missions is finding a balance of enemy ships where the player actually feels that his base is in danger, without making the mission impossible. Strikal bombers like to attack in groups, and can deal massive damage if they break through the defenses. It is up to the player to be sure to break up these groups of bombers as soon as possible.
The screenshot below shows the aftermath of the first defense mission (3rd mission in the release game). Since this is an early and easy mission, I do not think the Revi bombers actually have enough firepower to take out the station. It is still fun to look at the damage on the tactical display and realize that your home base is not necessarily safe.