I voted exploration and discovery.
I would have voted "all of the above", but I realize that's impractical... each book needs to focus on a theme or era.
One thing I would really like to see is ajustments for vessel type, or even scenarios designed just for smaller ships. My group plays aboard a Nova class surveyor. It's an excellent ship, but doesn't have the resources a Galaxy or Nebula would.
After the exploration book I'd really love to see a DW adventure pack.
“I am a soldier. I fight where I am told, and I win where I fight.”
General George S. Patton, Jr.